Jobs at Sierra Space
244,429 open positions
Founded in 2020 as a spin‑off of Sierra Nevada Corporation, Sierra Space is building the world’s first fully reusable orbital habitat, the Sierra Space Orbital Platform, and the Sierra Space Transport system. The company partners with NASA on the Lunar Gateway and is developing hardware that will enable commercial space stations.
Sierra Space hires aerospace engineers, propulsion specialists, systems integration experts, software developers, and project managers, as well as manufacturing, quality assurance, supply‑chain, and business operations professionals. Candidates can expect to work on mission‑critical hardware in a fast‑paced, collaborative environment with a focus on safety, reliability, and the commercial viability of space products.
By reviewing Sierra Space listings on Job Transparency you gain immediate access to salary ranges, benefits, and employee sentiment scores. This data lets you compare offers, negotiate confidently, and assess whether the company’s compensation aligns with industry standards before you apply.
CNC Programmer
Company: Impulse Space
Location: Other US Location
Posted Nov 22, 2023
Impulse Space is an Equal Opportunity Employer; employment with Impulse Space is governed on the basis of merit, competence and qualifications and will not be influenced in any manner by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability or any other legally protected status. 4+ years of experience on 5-axis mills, 5-axis mill turns, live tooled turret lathes, etc. Individual level and base pay is determined on a case-by-case basis and may vary based on job-related skills, education, experience, technical capabilities and internal equity. To conform to U.S. Government space technology export regulations, including the International Traffic in Arms Regulations (ITAR) you must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State. Hands on experience on manual and CNC mills and/or lathes Ability to rapidly pick up new CAM software and manage large tool libraries Demonstrated high attention to detail and rapid pace of execution Preferred Skills and Experience Experience setting up machine shops, recommending and evaluating capital for purchase Past experience programming turbomachinery, experience programming in MAX-PAC Python programming experience or similar Additional Information: Compensation bands are determined by role, level, location, and alignment with market data. Constantly keep products moving and alerting management when bottlenecks are encountered Provide consistent ideas for process improvements Minimum Qualifications High school diploma or equivalency certificate 5+ years of CNC programming experience using various CAM packages (HSM Works, Fusion 360, ESPRIT, Hypermill, etc.) Learn more about the ITAR here. Responsibilities Fast pace of execution to deliver parts needed for engine, vehicle, avionics and test development Work with various CAM softwares (HSM Works, Fusion 360, ESPRIT, Hypermill, etc.) and strong ability to learn and become expert in new software rapidly Produce hardware on various machines and OEM software including Heidenhain, Okuma OSP, Siemens, Fanuc, etc.
Ground Software Engineer, Principal
Company: York Space Systems
Location: Greater Denver Area
Posted Dec 01, 2023
This policy applies to all terms and conditions of employment, including recruiting, hiring, placement, promotion, termination, layoff, recall, transfer, leaves of absence, compensation, and training. Security Clearance. Docker experience. York Space Systems provides equal employment opportunities to all employees and applicants for employment and prohibits discrimination and harassment of any type without regard to race, color, religion, age, sex, national origin, disability status, genetics, military or protected veteran status, sexual orientation, gender identity or expression, or any other characteristic protected by federal, state or local laws. Experience with multi-threaded applications. React and TypeScript. Strongly typed backend language, such as C or Java. Experience with SQL databases. Strong verbal and written communication, presentation, and interpersonal skills with the ability to work in a team environment. Familiarity with data visualization tools and Grafana.
Test Specialist
Company: Impulse Space
Location: Other US Location
Posted Nov 24, 2023
Impulse Space is an Equal Opportunity Employer; employment with Impulse Space is governed on the basis of merit, competence and qualifications and will not be influenced in any manner by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability or any other legally protected status. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State. To conform to U.S. Government space technology export regulations, including the International Traffic in Arms Regulations (ITAR) you must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. In addition to base salary, for full-time hires, you may also be eligible for long-term incentives, in the form of stock options, and access to medical, vision & dental coverage as well as access to a 401(k) retirement plan. Individual level and base pay is determined on a case-by-case basis and may vary based on job-related skills, education, experience, technical capabilities and internal equity. Learn more about the ITAR here. valves, actuators) Experience designing tooling in a hardware development environment Capable of solving complex problems with little to no supervision on schedule as an individual or as a member of an integrated team Additional Information: Compensation bands are determined by role, level, location, and alignment with market data. Responsibilities Fabricate, assemble and test high quality, high reliability propulsion components, combustion devices and electromechanical assemblies Perform verifications of flight hardware and document results in a clear, precise and complete manner Improve processes to enable automated acceptance testing Respond to production related non-conformances and drive to root cause and disposition Maintain process planning documents and action feedback when necessary Perform maintenance and calibration activities for automated acceptance testing equipment Work with engineers to create 2D drawings from existing 3D models by applying established drawing specifications and standards Minimum Qualifications High school diploma or equivalency certificate 4+ years of experience working on propulsion or electronic assembly and/or test production environment or a bachelor's degree in an engineering field Preferred Skills and Experience Associate degree or bachelor's degree in mechanical, aerospace, or electrical engineering Demonstrated professional experience providing support for the production and test of highly complex components (e.g. Test Specialist Department: Propulsion Engineering Employment Type: Full Time Location: Redondo Beach Reporting To: Kevin Miller, VP of Propulsion Compensation: $30.00 - $45.00 / hour Description As a Test Specialist, you will perform testing of propulsion and avionics assemblies while working with a cross-discipline team to develop and execute state-of-the-art spacecraft testing operations.
Mission Design Engineer
Company: Impulse Space
Location: Other US Location
Posted Nov 22, 2023
Impulse Space is an Equal Opportunity Employer; employment with Impulse Space is governed on the basis of merit, competence and qualifications and will not be influenced in any manner by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability or any other legally protected status. Individual level and base pay is determined on a case-by-case basis and may vary based on job-related skills, education, experience, technical capabilities and internal equity. To conform to U.S. Government space technology export regulations, including the International Traffic in Arms Regulations (ITAR) you must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State. Learn more about the ITAR here. Minimum Qualifications Bachelor's degree in STEM with preference for Aerospace Engineering, Computer Science, Physics, or other similar degree area 2+ years of experience working in a technical role Demonstrated ability to communicate technical material clearly and professionally Demonstrated working knowledge of orbital mechanics and spacecraft operations Demonstrated proficiency in at least one programming language with a preference for Python Preferred Skills and Experience Master's degree in a technical area Experience operating spacecraft on orbit Experience in one or more customer-facing roles General familiarity with the space industry Demonstrated ability to operate in a startup environment Experience with creating or using physics simulations Experience using typesetting software such as LaTeX Demonstrated ability to automate functionality of Microsoft suite tools (using VBA or other method) Additional Information: Compensation bands are determined by role, level, location, and alignment with market data. Responsibilities Create mission designs which efficiently accomplish the stated goals of potential customers Maintain familiarity with the technical performance capabilities of Impulse's space vehicles Develop tools to efficiently analyze, interpret, and present mission design results Assist in the effort of incorporating mission design technical details into written proposals Meet with customers to collect requirements and hear feedback regarding proposed mission designs Analyze proposed mission designs for effectiveness and identify areas of improvement Assist the Engineering team in the effort to continuously improve the spacecraft simulation and trajectory optimization software suite Work closely with other Product and Business Development team members to understand the needs of each customer and agree on the best approach for each proposal opportunity Examples of technical effort the mission design process may include: high-level CONOPs creation, preliminary trajectory optimization, requirements compliance verification, propellant budgeting, power budgeting, link budgeting, etc. Some travel to interface directly with customers may be required. This role will support proposal development and help ensure the mission designs and solutions proposed to customers are technically sound. This role is part of the Product and Business Development team but will require working closely with multiple teams including the Engineering team.
Sr. Propulsion Engineer
Company: ABL Space Systems
Location: El Segundo
Posted Nov 21, 2023
As such, US person status (including US citizens, permanent residents, asylees, and refugees) is a required qualification for this position. All qualified applicants will receive consideration for employment without regard to race, color, religion, sex (including pregnancy), sexual orientation, gender identity and/or expression, national origin, protected veteran status, disability, genetics, or citizenship status (when otherwise legally authorized to work and access export-controlled data) and will not be discriminated against on the basis of such characteristics or any other status protected by the laws or regulations in the locations where we operate. You will own and maintain engine system schematics, balances, and sequences, and make decisions quickly and effectively. RESPONSIBILITIES: Plan, lead and own complex test campaigns with little oversight Lead post-test data review, working closely with component owners to inform engine performance Use the engine balance to predict and analyze engine performance Own all hardware documentation and procedures Work with test technicians to integrate test articles, update and maintain hardware configuration Author and maintain automated test sequences Design and build test stands Monitor live test data on-console to evaluate engine health during test operations Disseminate learnings from testing to drive upgrades to components or stage BASIC QUALIFICATIONS: B.S. We encourage applicants of all ages. Engineers on the Engine RE team are highly motivated, proactive individuals who hold the highest level of accountability and drive a fast-paced environment at ABL’s test sites. in any engineering discipline from an accredited university 7+ years of industry experience in a propulsion test or analysis role PREFERRED SKILLS AND EXPERIENCE In-depth understanding of compressible/incompressible flow and thermodynamics Experience writing and executing test procedures and/or autosequences for complex hardware operations Pump-fed liquid rocket engine test data analysis 1-D fluid simulation or engine balance tools (ROCETS, GFSSP, AMESIM etc) Strong technical writing and communication skills with experience writing test plans and executing readiness reviews Ability to program scripts in Python WHAT WE LOOK FOR: Critical thinking: ABL engineers understand the “why” behind all design decisions, operational events and test outcomes Ability to deal with ambiguity: ABL engineers must be comfortable defining their own pathway to an objective End-to end ownership: projects are delivered fully complete and ready for flight ADDITIONAL REQUIREMENTS: The Propulsion Engineer, Engine Test must be willing to travel to launch and test sites to support integration and test work PHYSICAL REQUIREMENTS/WORK ENVIRONMENTS: Ability to sit or stand for extended periods of time Ability to use a computer to complete assignments Ability to communicate with individuals and groups in person, by phone and telepresence While performing the duties of this job, the employee will typically work in an office environment ITAR Requirement This position requires access to information protected under US export control laws, including the International Traffic in Arms Regulations and/or the Export Administration Regulations. Equal Opportunity Employer We are an equal opportunity employer. As aSeniorPropulsion Engineer, on the Engine RE team you will work closely with the Launch & Test team and the Test Technician team to drive integration and test schedules that quickly buy down risk on ABL’s engine systems across development, qualification, and acceptance testing. A Senior Propulsion Engineer on the Engine RE team is responsible for planning and execution of engine testing at ABL, from formulating initial test plans, to making Go/No-Go calls on console for engine hot-fires, performing data reviews, and leading anomaly investigations.
Ground Software Engineer, Lead
Company: York Space Systems
Location: Greater Denver Area
Posted Dec 01, 2023
This policy applies to all terms and conditions of employment, including recruiting, hiring, placement, promotion, termination, layoff, recall, transfer, leaves of absence, compensation, and training. Security Clearance. Docker experience. York Space Systems provides equal employment opportunities to all employees and applicants for employment and prohibits discrimination and harassment of any type without regard to race, color, religion, age, sex, national origin, disability status, genetics, military or protected veteran status, sexual orientation, gender identity or expression, or any other characteristic protected by federal, state or local laws. Experience with multi-threaded applications. React and TypeScript. Strongly typed backend language, such as C or Java. Experience with SQL databases. Strong verbal and written communication, presentation, and interpersonal skills with the ability to work in a team environment. Familiarity with data visualization tools and Grafana.
Embedded Software Engineer
Company: Impulse Space
Location: Other US Location
Posted Nov 22, 2023
Impulse Space is an Equal Opportunity Employer; employment with Impulse Space is governed on the basis of merit, competence and qualifications and will not be influenced in any manner by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability or any other legally protected status. Individual level and base pay is determined on a case-by-case basis and may vary based on job-related skills, education, experience, technical capabilities and internal equity. To conform to U.S. Government space technology export regulations, including the International Traffic in Arms Regulations (ITAR) you must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. Responsibilities Implement and improve low-level processor functions such as controls of peripherals, and setup of communication interfaces Implement and improve functions such as closed loop control of physical processes, and detection/response algorithms for failures such as broken sensors or radiation upsets Provide technical input on new system developments from an embedded software perspective Write scrappy code to support development testing of avionics, fluids, and propulsion devices Write rigorous, reviewed, and tested code to support manufacturing and flight Minimum Qualifications Bachelor's degree in Computer Engineering, Electrical Engineering, Computer Science, or related degrees 3+ years' writing C/C++ code for an embedded system or vehicle of some kind (robot, car, drone, spacecraft, etc) Experience using spectrum-analyzers, oscilloscopes, logic analyzers, hardware debuggers, and source-level debuggers to troubleshoot problems at all layers of the stack Knowledge of and experience with communication protocols including I2C, CAN, SPI, and UART Good fundamentals in signal processing, classical control theory, and excellent problem-solving skills Experience working collaboratively across teams in a mixed software/hardware environment Preferred Skills and Experience Experience working with Software Defined Radios (SDR) Experience with digital filter design such as FIR, IIR, and adaptive filters Experience developing RF signal modulation and demodulation algorithms such as QPSK, BPSK, and GFSK Familiarity with RF concepts such as SNR, OIP3, IIP3, Phase Noise, Nyquist, etc Experience with using RF Test equipment for RF validation and debugging Strong understanding of embedded software principles and ability to contribute to design reviews Additional Information: Compensation bands are determined by role, level, location, and alignment with market data. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State. You will have the opportunity to contribute to many aspects of spacecraft development, including architecting new systems, doing quick prototypes, doing rigorous flight projects, and controlling flight hardware during ground tests. You will work with avionics hardware engineers, GNC engineers, propulsion engineers, and others to develop performant and maintainable solutions. Learn more about the ITAR here. Embedded Software Engineer Department: Autonomous Systems Employment Type: Full Time Location: Redondo Beach Reporting To: Atta Kashmiri, Lead Software Engineer Compensation: $115,000 - $195,000 / year Description As an Embedded Software Engineer your core responsibility will be to write code that runs on custom avionics hardware for executing flight and ground test functions.
Ground Software Engineer, Senior
Company: York Space Systems
Location: Greater Denver Area
Posted Dec 01, 2023
This policy applies to all terms and conditions or employment, including recruiting, hiring, placement, promotion, termination, layoff, recall, transfer, leaves of absence, compensation and training. Experience with modern state management tools such as Recoil.js, React Query, Mobx, etc. York Space Systems provides equal employment opportunities to all employees and applicants for employment and prohibits discrimination and harassment of any type without regard to race, color, religion, age, sex, national origin, disability status, genetics, military or protected veteran status, sexual orientation, gender identity or expression, or any other characteristic protected by federal, state, or local laws. React using TypeScript. Experience with common front-end development tools such as Babel, Webpack, NPM, etc. Strongly typed backend language, such as C or Java. YORK SPACE SYSTEMS IS AN EEO EMPLOYER. Strong verbal and written communication, presentation, and interpersonal skills with the ability to work in a collaborative team environment. Experience with SQL databases. Experience with modern security practices.
Ground Software Engineer
Company: York Space Systems
Location: Greater Denver Area
Posted Dec 01, 2023
This policy applies to all terms and conditions of employment, including recruiting, hiring, placement, promotion, termination, layoff, recall, transfer, leaves of absence, compensation, and training. Docker experience. Security Clearance. TypeScript experience. Experience with modern state management tools such as Recoil.js, React Query, Mobx, etc. York Space Systems provides equal employment opportunities to all employees and applicants for employment and prohibits discrimination and harassment of any type without regard to race, color, religion, age, sex, national origin, disability status, genetics, military or protected veteran status, sexual orientation, gender identity or expression, or any other characteristic protected by federal, state or local laws. Experience with multi-threaded applications. Experience in React.js. Strongly typed backend language, such as C or Java. Strong verbal and written communication, presentation, and interpersonal skills with the ability to work in a team environment.
SaaS Sales AE - Fully Remote
Company: Sierra Interactive
Location: Louisville, KY
Posted Nov 24, 2023
Talk to us. Demonstrate advanced knowledge of the real estate industry, real estate technology solutions, as well as the Sierra Interactive value proposition. Come prepared to talk numbers. While hitting numbers is important, we also value team players who are naturally curious, driven and accountable. Use a consultative sales approach to understand and assess client pain points, product requirements, and fit, and provide recommendations and solutions to ensure customer readiness to onboard, adopt the products, and be successful Skillfully answer questions during the sales process and manage objections and negotiations Ensure a seamless and successful hand-off to onboarding and Customer Success Identify and collaborate with Customer Success on customer expansion opportunities to drive product adoption, white space revenue, and retention Leverage marketing assets and sales enablement tools effectively in the sales process Own monthly sales targets and relevant metrics; report and record all relevant data in HubSpot CRM Travel occasionally to attend sponsored events in the U.S. and Canada where you'll identify key prospects and follow up with leads to ensure ROI on the event The expected ramp rate is three months Requirements 2+ years of B2B or SaaS sales experience with proven success. Bachelor's degree or equivalent experience Be a resident of the U.S. A private, quiet office free of distractions with good lighting and acoustics Impeccable, polished communication and online presentation skills, including demo experience Exceptionally driven with an eye for detail and a focus on results Superior relationship-building and negotiation skills Track record of meeting/exceeding quotas in a high-velocity environment Tech-savvy with experience using CRM and sales enablement software (Kixy, Video Messaging) Ability to learn quickly, act independently, and multi-task in a remote environment Bonus points if: You have real estate vendor industry experience If you are proficient in HubSpot CRM Benefits 100% remote work Competitive compensation and commission structure Paid holidays and paid time off Excellent medical, dental and vision coverage with full cost covered for employee and the option to add spouse/partner and dependents 401k retirement employer matching contributions up to 4% A respectful and open work environment Something else important to you? We're flexible and committed to providing a healthy work environment where great people can thrive. Requirements Day-to-Day you will: Identify and proactively prospect real estate brokers and teams who fit our ideal customer profile and handle inbound leads assigned to you, converting them into successfully closed deals. This position reports directly to the Director of Sales and Partnerships. This requires impeccable communication and pipeline management.
Senior Propulsion Engineer
Company: Impulse Space
Location: Other US Location
Posted Dec 03, 2023
Impulse Space is an Equal Opportunity Employer; employment with Impulse Space is governed on the basis of merit, competence and qualifications and will not be influenced in any manner by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability or any other legally protected status. To conform to U.S. Government space technology export regulations, including the International Traffic in Arms Regulations (ITAR) you must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State. In addition to base salary, for full-time hires, you may also be eligible for long-term incentives, in the form of stock options, and access to medical, vision & dental coverage as well as access to a 401(k) retirement plan. Individual level and base pay is determined on a case-by-case basis and may vary based on job-related skills, education, experience, technical capabilities and internal equity. Learn more about the ITAR here. Responsibilities Serve as Responsible Engineer for spacecraft propulsion systems including programmatic ownership of related fluids, mechanical, electrical and controls systems Work with wide ranging teams across engineering, manufacturing and procurement to deliver reliable and efficient propulsion systems Manage interface with external customers and drive toward shared mission success Ensure that the performance and function of hardware meets intent by performing analysis and design reviews Perform system validation test preparation, planning and execution Resolve technical issues with innovative resourceful solutions Minimum Qualifications Bachelor's degree in engineering or science 5+ years of demonstrated experience in the aerospace propulsion field Proficiency in basic principles of fluids, thermodynamics, heat transfer, mechanics and materials Hands-on experience working with fluid, mechanical, electrical and controls systems Demonstrated ability in conceptual design, fabrication and testing of hardware Demonstrated ability of taking project ownership and working collaboratively with small teams Preferred Skills and Experience Master's degree in aerospace or mechanical engineering Prior experience working on all phases of a spaceflight propulsion system Prior experience working with cryogenic propellants, saturated fluids and liquid rocket propulsion development Familiarity with NASA and DoD standards regarding spaceflight propulsion specifications and standards Experience in a startup or agile development environment Additional Information: Compensation bands are determined by role, level, location, and alignment with market data. Senior Propulsion Engineer Department: Propulsion Engineering Employment Type: Full Time Location: Redondo Beach Reporting To: Kevin Miller, VP of Propulsion Compensation: $140,000 - $190,000 / year Description As a Senior Propulsion Engineer at Impulse Space, you will own all aspects of propulsion system hardware design, analysis, implementation and operation while working closely with a fast paced, agile team that produces high-performance spacecraft from clean sheet designs.
Embedded Software Engineer
Company: Impulse Space
Location: Other US Location
Posted Nov 22, 2023
Impulse Space is an Equal Opportunity Employer; employment with Impulse Space is governed on the basis of merit, competence and qualifications and will not be influenced in any manner by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability or any other legally protected status. Individual level and base pay is determined on a case-by-case basis and may vary based on job-related skills, education, experience, technical capabilities and internal equity. Experience with digital filter design such as FIR, IIR, and adaptive filters Prior experience with motor controller functionality, behaviors, and algorithms Experience with PWM motor drivers, PID controllers, and ARM Processors Strong understanding of embedded software principles and ability to contribute to design reviews Additional Information: Compensation bands are determined by role, level, location, and alignment with market data. To conform to U.S. Government space technology export regulations, including the International Traffic in Arms Regulations (ITAR) you must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. Responsibilities Implement and improve low-level processor functions such as controls of peripherals, and setup of communication interfaces Implement and improve functions such as closed loop control of physical processes, and detection/response algorithms for failures such as broken sensors or radiation upsets Provide technical input on new system developments from an embedded software perspective Write scrappy code to support development testing of avionics, fluids, and propulsion devices Write rigorous, reviewed, and tested code to support manufacturing and flight Minimum Qualifications Bachelor's degree in Computer Engineering, Electrical Engineering, Computer Science, or related degrees 3+ years' writing C/C++ code for an embedded system or vehicle of some kind (robot, car, drone, spacecraft, etc) Experience using spectrum-analyzers, oscilloscopes, logic analyzers, hardware debuggers, and source-level debuggers to troubleshoot problems at all layers of the stack Knowledge of and experience with communication protocols including I2C, CAN, SPI, and UART Good fundamentals in signal processing, classical control theory, and excellent problem-solving skills Experience working collaboratively across teams in a mixed software/hardware environment Preferred Skills and Experience Familiarity with RF concepts such as Power, Voltage, Gain, OIP3, IIP3, Phase Noise, etc. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State. You will have the opportunity to contribute to many aspects of spacecraft development, including architecting new systems, doing quick prototypes, doing rigorous flight projects, and controlling flight hardware during ground tests. You will work with avionics hardware engineers, GNC engineers, propulsion engineers, and others to develop performant and maintainable solutions. Learn more about the ITAR here. Embedded Software Engineer Department: Autonomous Systems Employment Type: Full Time Location: Redondo Beach Reporting To: Atta Kashmiri, Lead Software Engineer Compensation: $115,000 - $195,000 / year Description As an Embedded Software Engineer your core responsibility will be to write code that runs on custom avionics hardware for executing flight and ground test functions.