Nuclear thermal · single stage · runway to runway
A cab
to orbit
A small spaceplane with a nuclear thermal engine. It takes off from a 5,000 ft runway, drops 180 kg into a 400 km orbit, glides home and flies again 72 hours later.
- Clean exhaust
- HALEU < 20% U-235
- Isp 1,000 s
- SSTO · HTHL
The wall
Chemical rockets top out at 450 seconds.
Specific impulse is how far a kilogram of propellant pushes you. Burning hydrogen with oxygen caps out around 450 s, which is why rockets are mostly tank and throw most of themselves away. Heating hydrogen in a reactor instead of burning it roughly doubles that. Doubled Isp is the difference between staging and flying to orbit in one piece.
The engine
Hot hydrogen. Clean exhaust.
Hydrogen never touches the uranium. A thin tungsten liner sits between the fuel and the flow, so what leaves the nozzle is hot hydrogen and nothing else. That makes it legal to fly from a runway.
- MITEE-C Reactor core
65 cm · 61 fuel elements · W-UO₂ cermet - HALEU-20 Fuel
< 20% U-235 · not weapons grade - W-LINER Tungsten liner
Keeps fuel out of the exhaust - CD-12 Control drums
12 × Be / B₄C · k_eff 1.033 → 0.913 - SH-CE7 Shield
7 cm cyanate ester · 222 kg - DOSE-25 Public dose
< 25 mrem at the 1 km fence
Live simulation · take the stick
Runway to orbit, in your browser.
This is not a video. The spaceplane rolls down a runway at Cape Canaveral, climbs on the SBIR attitude program (38° to 0° by 50 km), reaches orbital speed, circularises at 400 km, deploys its payload and deorbits. The physics is real: rotating Earth, the US Standard Atmosphere, lift and drag, 6 kg/s of hydrogen burned one tenth of a second at a time. The cyan ghost is the plan. Hit “Fly it” to take over and “Rejoin” to hand back to the flight computer.
Your mission table, flown in 3D
| Stage | SBIR · kg | 3D sim · kg |
|---|---|---|
| Takeoff | 51.50 | 54.00 |
| Atmospheric manoeuvre | 3,458.40 | 3,525.60 |
| Hohmann burn 1 | 25.60 | 30.64 |
| Hohmann burn 2 | 25.55 | 38.13 |
| Deorbit burn | 13.23 | 11.99 |
| Left in the tank | 103.73 | 16.98 |
Climb ends at 50.23 km and 7.888 km/s inertial, T+597 s (SBIR: 50.23 km, 7.88 km/s, T+585 s).
Takeoff, climb end and deorbit land on your numbers. The reserve is where it gets interesting: the mission closes on 104 kg — 2.8 % of the propellant — and a 3D climb that runs 12 s longer, plus a Hohmann transfer that starts inside 28 kPa of air, spends most of it. How sensitive is closure to the climb in your model? We’d love to compare notes.
The flight ends at the 200 km perigee, like the report. Reentry and the glide home aren’t modelled yet.
› Run it yourself — change any number, sweep, download the data ↗Mass, thrust, Isp, aero areas and the mission profile come from CubeCab’s SBIR Phase I report. The lift-curve slope, reactor response time and launch site are illustrative assumptions — swap in your own and the sim becomes a design tool.
The fare
Metered like a cab. Priced like a bus.
100 flights a year
One vehicle, two launches a week. Refuel with hydrogen and go. No stages to recover and no booster to rebuild.
Your orbit, not a rideshare
A dedicated ride to the altitude and inclination you need, on your schedule.
Runway, not a pad
Horizontal takeoff and landing. A 5,000 ft strip replaces a launch complex.
Fuel is cheap
Hydrogen at about $50 per kilogram all in. HALEU cores are swapped every four years.
CubeCab
Space access for the rest of us.
CubeCab started by building the smallest launcher for 3U CubeSats: dedicated rides at a price universities and startups can afford. The nuclear thermal spaceplane is the same mission at scale. A DOE SBIR Phase I study concluded it is probably feasible, both technically and under US regulation.
Supported by
- U.S. Department of Energy · SBIR Phase I