SPACE INDEX COMPANIES INSIGHTS SECTORS PRODUCTS NEWS BLOG ANSWERS RESEARCH ABOUT FOR COMPANIES BUILD / 2026.06.04
Phase Four logo Phase Four Developed electrodeless radio-frequency and multi-mode electric propulsion systems for satellites vs Sierra Space Designs and manufactures satellite platforms, reusable spaceplanes, expandable habitats, and propulsion systems for national security and civil space Sierra Space logo
HEAD-TO-HEAD1 shared sector
Phase Four Sierra Space
Founded 2015 2021
Headquarters Hawthorne, California Louisville, Colorado
Type private private
Status closed operating
Employees 5 1,072
Total funding $35.8M $2.2B
Latest round Series C Series C
Sectors Space Propulsion, Satellite Components & Subsystems Satellite Manufacturing, Space Propulsion, Space Stations & Habitats
Products listed 4 7
Federal contracts 1 ($6.5M)
Launches
Leaders listed Steve Kiser, M. Umair Siddiqui, Simon Halpern Dan Jablonsky, Janet Kavandi, Troy Lahr
News mentions 0 0
SHARED SECTORS
FREQUENTLY ASKED

How do Phase Four and Sierra Space compare?

Both companies work in Space Propulsion. Phase Four was founded in 2015 and Sierra Space in 2021.

Which is larger, Phase Four or Sierra Space?

Sierra Space reports the larger workforce, with 1,072 employees versus 5.

Which has more US federal contracts, Phase Four or Sierra Space?

Sierra Space has been awarded more, with $6.5M across 1 awards.

Numbers refresh on every render against the live Space Index database. Federal contract data from USAspending.gov; launches from LaunchLibrary2.