-4.66 calibers · limit not a stability requirement for this class
An orbital launcher is aerodynamically unstable on purpose. Fins big enough to stabilise a vehicle this slender would be dead mass carried the whole way up, and they would fight the gravity turn rather than help it, so real launchers do not have them: Falcon 9, Atlas V and Electron all fly with the centre of pressure ahead of the centre of gravity. What keeps the nose forward is thrust vector control — the engines gimbal a few degrees and the vehicle balances on its own thrust, the way a broom balances on a palm. This simulation does not model that control loop, so it cannot tell you whether the gimbal has enough authority; it can only tell you that static margin is the wrong question to ask here.
Fix: Nothing to fix. Static margin is a criterion for unguided fin-stabilised rockets.
Flight simulation
On the pad. Press Launch to integrate the ascent and descent and fly this design.
Stability
Where this can go
14.39 km/s ideal ΔV
Furthest reachable: The main belt.
- ▸ Low Earth orbit9.40 km/s+4.99 km/s
Reachable with room to spare. Where everything starts. The ISS, most satellites, and the hardest single step of any mission — more than half the budget of a trip to Mars is spent just getting here.
- ▸ Geostationary transfer11.84 km/s+2.55 km/s
Reachable with room to spare. An ellipse out to 35,786 km. Circularising at the top costs a further 1.5 km/s that this figure does not include.
- ▸ The Moon12.52 km/s+1.87 km/s
Reachable with room to spare. Trans-lunar injection. Cheaper than Mars, and three days rather than seven months.
- ▸ Earth escape12.62 km/s+1.77 km/s
Reachable with room to spare. C3 = 0: enough to never come back, arriving at infinity with nothing left. Only 100 m/s more than reaching the Moon.
- ▸ Mars13.00 km/s+1.39 km/s
Reachable with room to spare. Trans-Mars injection on a Hohmann transfer. Departure windows open roughly every 26 months, when the two planets line up correctly.
- ▸ The main belt14.30 km/s+0.09 km/s
Reachable on paper only — thinner than the losses a real mission pays. Ceres and Vesta. Far enough out that solar panels start to struggle and most missions carry a different power source.
- · Jupiter15.70 km/s−1.31 km/s
- · Saturn16.70 km/s−2.31 km/s
- · Out of the solar system18.20 km/s−3.81 km/s
Beyond the solar system
This design stays bound to the Sun, so none of it is open. Leaving costs 18.20 km/s from the ground and this has 14.39 — 3.81 km/s short. Every probe that has actually left took the difference from a planet rather than from its own tanks.
A coast at the speed left after escaping both the Earth and the Sun, with no gravity assists and — more importantly — no deceleration at the far end. These are flyby times at full speed, for a vehicle assumed to survive the trip, which nothing built has come close to doing. Every one of them is therefore the optimistic figure.
Direct transfers, with no gravity assists. That is the honest answer to “can this vehicle do it alone” and the pessimistic answer to “can this be done” — Voyager 2 reached Neptune on a budget that would not have reached Jupiter directly, by taking angular momentum from every planet it passed. Cassini spent seven years and four assists rather than pay Saturn's direct price.
Inside
Derived from the design rather than drawn: every band is at its real station and every tank is sized from the propellant mass it holds divided by that propellant's real density. Scrub along the vehicle to see what is around you at any point.
Cutaway · airframe 21.60 m
length to scale · radius ×2.4
Onboard at 7.13 m
Looking forward. Rings are the real radii at this station, to scale with each other.
What is around you
- Upper stage — LH₂ tank428.6 kginferred
429 kg of fuel at a 6:1 oxidiser-to-fuel ratio. Forward of the oxidiser, so the heavier tank sits lower and the vehicle is easier to steer.
V = (m/ρ)(1+u) = 6.23 m³ → L = V/πr² = 3.10 m
Innermost here: Upper stage — LH₂ tank. Static margin -4.66 calibers — the CP must stay aft of the CG or the airframe flies backwards.
- Kick stage: 450 s vacuum Isp implies hydrolox — nothing else reaches 400 s. Its LH₂ tank is 2.7× the volume of its LOX tank despite holding 6× less mass, because liquid hydrogen is 16× less dense than liquid oxygen.
- Upper stage: 450 s vacuum Isp implies hydrolox — nothing else reaches 400 s. Its LH₂ tank is 2.7× the volume of its LOX tank despite holding 6× less mass, because liquid hydrogen is 16× less dense than liquid oxygen.
Where to get it
Two ways in: build what you designed from raw stock, or buy a starter set and fly something tonight. The parts below are matched to the design above.
Self dev · what this design needs
3 items
Matched to the design above: the tube size comes from its diameter, the motor mount from its casing, the fin stock from its thickness, and the certification gate from its total impulse. Change the design and these change.
Airframe
- Propellant tank — 1.6 m diameter
aluminium-lithium, friction-stir welded
At this scale the tank wall IS the airframe, and it is pressure-stabilised — it holds its own shape only because it is pressurised, which is why an empty one can collapse under its own weight.
No consumer source. Al-Li 2195 plate comes from a mill in quantity, and the longitudinal welds need friction-stir equipment. As a launch-vehicle component it is export-controlled under ITAR. In practice nobody buys a stage: you buy a launch.
- Payload — 150 kg
the only mass that matters
Everything else on the vehicle exists to put this into orbit. For a smallsat this is the one line item that IS commercially available, as a CubeSat bus and a launch contract.
CubeSat buses and rideshare slots are genuinely purchasable, unlike the stage beneath them. That asymmetry is the real state of the industry: the ride is a product, the rocket is not.
Propulsion
- Liquid rocket engine
450 s vacuum Isp
The turbopump is the hard part, not the chamber — it moves propellant at hundreds of kilograms a second against several hundred bar, and it is where most engine programmes spend their schedule.
No consumer source, and no realistic fabrication route for an individual. Export-controlled. The honest acquisition path for a payload this size is a rideshare booking, which is a contract rather than a part.
The minimum to fly once, and deliberately not matched to your design — its purpose is to remove every decision rather than to match a drawing. A launch set is already stable and its rod already fits, so nothing here needs checking. Four of these five are sold separately from the box.
No affiliation with any vendor listed and no commission on anything bought. Links go to a vendor's own search for a part type, not to a specific product, because product links and prices both go stale — check current price and stock yourself. Standard sizes shown are the common ones, not a full catalogue: “non-standard” means “not in this list”, which is a prompt to check rather than a verdict.
Forces in ascent
Fusion, for reference — not fitted to anything above
The cruise stage on this page collects its power from sunlight. These curves are the alternative nobody has flown: carrying the power source. They are here because the numbers explain why — and they are wired to no vehicle on this page, deliberately. No rocket in this app fuses anything.
Loading the Bosch & Hale curves…
NAR Model Rocket Safety Code
- Lightweight, non-metallic construction only — paper, cardboard, balsa wood, or plastic.
- Certified, commercially-made motors only — never tampered with, modified, or home-built.
- Launcher pointed within 30° of vertical (see the Launch angle field above).
- Launch outdoors, in an open area sized to the rocket's power, in safe weather.
- Every rocket carries a working recovery system — parachute or streamer.
FAA amateur-rocket classes (14 CFR § 101.22)
- Class 1 — Model Rocket: ≤125 g propellant, slow-burning, non-metal construction, ≤1,500 g total liftoff weight.
- Class 2 — High-Power Rocket: combined motor total impulse ≤40,960 N·s (9,208 lbf·s).
- Class 3 — Advanced High-Power Rocket: beyond Class 2.
- Every amateur rocket, any class, must stay suborbital, unmanned, under 150 km apogee, and under 889,600 N·s total impulse.
Tripoli high-power certification
- Level 1: up to 640 N·s total impulse (H/I-class motors).
- Level 2: up to 5,120 N·s (J/K/L-class motors).
- Level 3: M-class and above, no upper limit.
Where this simulator fits, and where to go next
- NASA Beginner's Guide to Rockets — the four forces, thrust, drag, and stability, the same fundamentals this simulator computes with the Barrowman method.
- OpenRocket — the natural next tool once you outgrow this proof of concept: a full component-based design/simulation package with 2D/3D views and a real parts database.
- Build a real model rocket around a certified, commercial motor, and fly it at an NAR club launch.
- Build up the physics and calculus background behind the equations this app already cites.
- MIT 16.512 Rocket Propulsion and 16.522 Space Propulsion — nozzle design, combustion thermochemistry, and orbital maneuvers, using Rocket Propulsion Elements (Sutton & Biblarz) and Mechanics and Thermodynamics of Propulsion (Hill & Peterson) as the standard texts.
- High-power certification through Tripoli (above), for motors beyond consumer model-rocket scale.
- University-scale aerospace projects — structures, avionics, guidance/navigation/control, orbital mechanics.
At every step, propulsion stays on certified commercial motors — building or modifying propellant yourself falls outside every safety code linked above.