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Phase Four

Type: VC-backed startup (independent) Location: El Segundo, CA Founded: ~2015 Product: Maxwell RF plasma thruster (Block 1/2/3), Valkyrie family, multi-mode propulsion systems PI (SST): Sidhu Jesse (ASCENT project), Ali Guarneros Luna (GRC lifetime testing)

Last updated: 2026-04-14 (session 34)

SST Projects (2)

Both SST projects used the Announcement of Collaboration Opportunity (ACO) mechanism — NASA provides facilities and expertise at GRC/MSFC; Phase Four provides hardware. SST funded NASA center effort, not Phase Four directly.

Lifetime Trend Testing of the Phase Four RF Thruster — 106833

  • TRL: 6→8 | Period: 2020-12 → 2024-10
  • Lead: Glenn Research Center (GRC) | Phase Four as partner
  • 1,000+ hours of lifetime testing at GRC vacuum facilities. Determined degradation rates and failure modes. Results fed into product lifetime predictions for commercial customers.
  • View count: 3,434 — highest of any SST propulsion project, suggesting broad interest.
  • No TechPort documents attached.

ASCENT Gas Feed System for RF Thruster — 155356

  • TRL: 3→6 (target) | Period: 2023-04 → 2026-01
  • Lead: Phase Four LLC | Marshall SFC as partner
  • Electrolytic propellant decomposition chamber (PDC) to convert ASCENT green propellant into gas for RF thruster. Enables dual-mode propulsion: same ASCENT tank feeds both high-thrust chemical thruster and high-Isp RF electric thruster.
  • Parallel to AFRL STRATFI-TACFI work on catalytic PDC (FA930023C6025, $1.78M).
  • No TechPort documents attached.

TechPort Footprint

Only 1 TechPort project as lead org (155356). Project 106833 is GRC-led with Phase Four as partner. No SBIR/STTR pipeline in TechPort. Phase Four's R&D funding came primarily from DARPA and USAF, not NASA SBIR.

Upstream Lineage

Source Detail Confidence
DARPA 2015 NASA contract (NNA15BA42C) mentions "direct traceability to a larger DARPA" engine. DARPA funded the original RF thruster concept confirmed (USASpending description)
NASA ARC $950K contract (2015-08 → 2017-10) to design/build/qualify RF thruster on CubeSat confirmed (USASpending)
SST ACO (2020) GRC lifetime testing validated commercial product (TRL 6→8) confirmed
SST ACO (2023) MSFC ASCENT feed system — green propellant multi-mode confirmed
AFRL STRATFI-TACFI $1.78M for catalytic PDC (parallel to SST electrolytic PDC) confirmed (USASpending)

Federal Funding Footprint

USASpending ($9.8M+ across 9 awards)

Award ID Agency Amount Period Description
FA930025C6010 USAF $1.80M 2025-04 → 2026-12 Development of propulsion
FA930025C6024 USAF $1.80M 2025-09 → 2027-10 Flight development of ASCENT propellant
FA930023C6025 USAF (AFRL STRATFI-TACFI) $1.78M 2023-09 → 2025-12 Catalytic PDC for multi-mode propulsion
FA881021C0047 USAF (Space Pitch Day) $1.69M 2023-02 → 2023-04 Phase Four Space Pitch Day
N6600122C4009 Navy $979K 2022-01 → 2023-07 Research per SOW
NNA15BA42C NASA ARC $950K 2015-08 → 2017-10 Design/build/qualify RF thruster on CubeSat (DARPA traceability)
FA864921P0849 USAF $749K 2021-03 → 2022-12 High delta-v EP for small satellites
FA864920P0762 USAF $50K 2020-03 → 2020-06 SBIR feasibility — next-gen EP for small sats
FA864921P0685 USAF $46K 2021-04 → 2021-07 Low-cost high-power SEP

Total USASpending: ~$9.8M | NASA: ~$950K | DoD (USASpending): ~$8.9M DARPA Otter (not yet in USASpending): $14.9M Total identified federal: ~$24.7M | DoD share: ~$23.8M (96%)

Venture Funding ($43.6M total equity)

  • Series B: $26M (2021, led by New Science Ventures)
  • Series C: $12.9M (Jan 2025, led by Artemis Group Capital)
  • Total: $43.6M across 6 rounds (Crunchbase/Dealroom)

Downstream Impact

Flight Heritage

  • 9 satellites launched with Maxwell thrusters, 5,300+ days of cumulative on-orbit heritage as of Apr 2024. Confidence: confirmed (company press release, DARPA Otter announcement).
  • Maxwell Block 1 on Capella Space SAR satellite (SpaceX Transporter-2, June 2021): First electrodeless RF thruster to fly in space. On-orbit operation confirmed. Confidence: confirmed (press release).
  • Multiple Maxwell systems on orbit with commercial smallsat operators. Confidence: confirmed (press).
  • Maxwell Block 3 announced — claims to exceed Hall-effect thruster performance. Series C ($12.9M, Jan 2025) funds Block 3 scale-up. Confidence: suggestive (press announcement, no independent verification).

Commercial Products

  • Maxwell Block 1/2/3: Electrodeless RF plasma thrusters. No cathode, no high-voltage grids — mass-manufacturable. Propellant-agnostic (Xe, Kr, iodine, ASCENT).
  • Valkyrie family: Larger thruster variants.
  • Multi-mode propulsion: Single ASCENT or hydrazine tank feeds both chemical (high thrust) and electric (high Isp) modes. Ground demos with DoD partners by Q1 2025.
  • Subscription service for smallsat manufacturers (announced 2021).
  • Impulse Space collaboration on multi-mode propulsion.

Defense / National Security

  • Phase Four is heavily DoD-funded. Including DARPA Otter, DoD total is ~$23.8M (vs $950K NASA).
  • DARPA Otter program: $14.9M (awarded Apr 2024, 4-year contract) — air-breathing electric propulsion (ABEP) for Very Low Earth Orbit (90–450 km). Phase Four's RF thruster is propellant-agnostic, enabling it to ingest ambient atmospheric gas as propellant. Culminates in a long-duration on-orbit demonstration. This extends DARPA's founding role in Phase Four (DARPA originated the RF thruster concept ~2015) into a second major technology bet. Confidence: confirmed (PR Newswire, Apr 2024).
  • AFRL STRATFI-TACFI pipeline for ASCENT multi-mode propulsion.
  • Two USAF contracts in 2025 ($3.6M combined) for propulsion development and ASCENT flight demo.
  • Space Pitch Day winner ($1.69M).

Publications

  • NTRS: 0 citations found.

Assessment

Outcome category: commercialized | Confidence: confirmed

Phase Four is the DoD-dominant archetype in the SST portfolio. Unlike ExoTerra or Busek where NASA SBIR was the sustained R&D lifeline, Phase Four's primary funding came from DARPA (origin), USAF (scale-up), DARPA again (ABEP/VLEO), and VC ($43.6M). NASA's total contribution was ~$950K direct + SST ACO facility time at GRC and MSFC.

What SST funded: SST's contribution was facility access and test validation, not direct R&D funding. The GRC lifetime testing (1,000+ hours) gave Phase Four product lifetime data it couldn't get internally. The MSFC ASCENT work enabled the multi-mode capability. Both are the ACO pattern — NASA provides world-class test facilities; company provides hardware.

DARPA bookend (session 34): The $14.9M DARPA Otter contract for ABEP/VLEO closes a loop — DARPA created Phase Four (~2015), and a decade later DARPA is betting $14.9M on a next-generation application. The RF thruster's propellant-agnostic nature, which was commercially useful for xenon/krypton flexibility, becomes a fundamental enabler for air-breathing propulsion at 90–450 km. This is the strongest example in the SST portfolio of a technology whose core architectural advantage (electrodeless, propellant-agnostic) unlocked a mission class (VLEO persistence) that wasn't in the original design scope.

Key contrast with ExoTerra: Both are smallsat EP companies. ExoTerra was built on 10 NASA SBIRs → SST → defense production → acquired. Phase Four was built on DARPA → USAF → VC → independent. SST's role in each was fundamentally different: funding pipeline (ExoTerra) vs. test infrastructure (Phase Four). Total federal funding is now comparable ($24.7M Phase Four vs ~$20M+ ExoTerra pre-acquisition), but 96% of Phase Four's comes from DoD.