# Is SSTO viable on Mars?

I know that Single-Stage-to-Orbit is quite challenging from the surface of Earth, but it's relatively straightforward from the moon (as demonstrated by the Apollo LM). What about Mars? Let's assume in-situ fueling of methane-LOX.

• A follow up question could be "Is it desirable ?" – Antzi Apr 28 '16 at 16:27

## 2 Answers

It's definitely viable. By the rocket equation:

$∆v = v_e \ln \frac {m_0} {m_f}$

Methane-LOX gives an exhaust velocity around 3500m/s. Mars surface to orbit requires the expenditure of about 3800 m/s of ∆v.

So the ratio of initial (fully fueled) mass to final (fuel spent) mass need only be around:

$e^{\frac {3800} {3500}}$

or

$e^{1.09}$

or about 3:1 -- 2 tons of propellant per 1 ton of empty ship/payload.

This is as compared to an Earth-launched SSTO, which needs about 9500 m/s, about a 15:1 mass ratio for methalox!

• How does atmospheric drag factor in? – kgutwin Apr 29 '16 at 16:18
• Drag is included in the needed ascent ∆v figures. The exact ∆v required for ascent to orbit will vary substantially with the rocket's thrust-vs-time profile (faster ascent incurs slightly more drag, but much less gravity loss). The figures above are "typical", but Earth ascents will vary from something like 9200-10000 m/s with different launchers. The drag penalty portion is fairly small; for the Saturn V, drag accounted for around 50 m/s of the ∆v budget, and on a Mars ascent it will be far less due to the thinner atmosphere. – Russell Borogove Apr 29 '16 at 17:30

Yes. Though one vs. two stages is always a trade. From what I've seen from Mars Sample Return studies anyway, two stages is usually the winner, mainly due to mass and volume constraints.

• Likely SSTO wouldn't be much of trade-off. SSTO-and-anywhere-else though definitely would be. Even back to the surface. – SF. Apr 28 '16 at 19:32