SSTO Calculator (v1)

(Created October 2025)

NOTES: This is actually my second attempt at making a SSTO calculator.

The first was aborted after I went through the publicly available VentureStar specifications from the following documents:


1997 Specifications


1998 Specifications

After gathering all the information, I became frustrated because VentureStar was incapable of delivering ANY payload to LEO through simple "sanity check" calculations. Furthermore, even with selecting an unrealistically high ISP (455 seconds) for the RS-2200, the system could only deliver 12 metric tons to LEO.

Yet, Lockheed was claiming 25.4 MT to LEO; surely there was something I was missing in my calculations? Perhaps these simple calculations didn't work for estimating SSTO flight performance? In frustration, I gave up and shelved the project.

About a decade or more later in 2025, I unwittingly recreated my earlier attempts at a SSTO calculator in order to estimate the performance of SpaceX's Starship if it was a SSTO vehicle instead of an upper stage. Once I had that done, I tried to use my method to estimate VentureStar's performance, having forgotten my earlier work.

With the second datapoint of Starship helping me; I realized that VentureStar pretty much would not have worked -- that's why my decade-earlier calculations based off public figures were so frustrating.

PS: I also found this amusing tidbit from VentureStar: Single Stage to Orbit Reusable Launch Vehicle Program Overview:

"Once financial debt has been paid off, VentureStar will be able to offer payload launch costs at an order of magnitude far below today's launch costs ($1,100 to $2,200/kg.)"

That debt pay-off goal was set for 2015. As of 2024, the price for Falcon 9 on a pre-booked mission to LEO is about $2,720/kg.

Payload to Orbit (metric tons)
  • Embraer ERJ 140LR Regional Jet: 5.29 MT
  • Embraer E175 Regional Jet: 10.1 MT
  • Boeing 737-300BCF: 20.76 MT
  • VentureStar ('98): 25.4 MT to LEO (185.2 km @ 28.5)
  • Boeing 777-300ER SF: 101.6 MT
Average Engine ISP (seconds)
  • RS-2200 Aerospike: 435 sec Average (347 SL, 455 vac)
  • RS-25 SSME: 409 sec Average (366 SL, 452 vac)
  • Raptor 3 (Mixed SL/Vac): 365 sec Average (350 SL, 380 vac)
  • Merlin 1D (Mixed SL/Vac): 329.5 sec Average (311 SL, 348 vac)
Propellant Mass (metric tons)
  • Falcon 9 Block 5 Booster: 410.9 MT
  • VentureStar ('98): 1050.3 MT
  • Starship v1: 1200 MT
  • Starship v2: 1500 MT
  • Starship v3: 1600 MT
  • Starship v4: 2300 MT

NOTE: In our performance calculations, we assume that 1.5% of propellant is unusable and cannot be burned; being added to dry mass.

Dry Mass (metric tons)
  • Falcon 9 Block 5 Booster: 22.2 MT
  • VentureStar ('98): 114.3 MT
  • Starship v1: 120 MT
Propellant Mass Fraction (pmf)
  • Falcon 9 FT Upper Stage: 0.965
  • Falcon 9 FT Booster: 0.951
  • Atlas V Core Stage: 0.93~
  • Ares V EDS: 0.916
  • Ares V Core Stage: 0.897
  • S-IVB: 0.884

------Performance------

GLOW (tonnes)
GLOB (tonnes)
Delta-V (m/sec)
  • Earth: 9500 m/sec
  • Mars: 3900 m/sec
  • Kerbin: 3500 m/sec (Kerbal Space Program)
  • Moon: 1800 m/sec

NOTE: All values are "sandbagged" with 100 m/s extra for atmospheric losses, etc.

------Estimated Costs------

Propellant Cost ($/Metric Ton)
  • LOX/LH2 @ 5.5 O/F Ratio (RS-2200): $2,220~/MT in 2025
  • LOX/CH4 @ 3.6 O/F Ratio (Raptor): $440~/MT in 2025
  • LOX/RP-1 @ 2.372 O/F Ratio (Merlin 1D): $349~/MT in 2025
Cost of SSTO (Millions $)
Lifetime of SSTO (Missions)
Amortization Rate Per Flight (Millions $)
Propellant Cost ($)

Range Ops/Labor Costs/Flight (Millions $)

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Payload Costs ($/kg)
  • SpaceX Falcon 9 Rideshare ($6500/kg) @ 2025
  • SpaceX Falcon 9 LEO ($2,720/kg) @ 2024
Total Cost to Launch Per Flight ($M)