# Propellant consumption of Starship trip from NRHO to Mars

People, I am trying to estimate the amount of propellant (liquid oxygen+ liquid methane) required by Starship to reach Mars from NRHO (Near-rectilinear halo orbit).

Also the propellant consumption profile will look different if starship wants to just orbit around Mars vs actually land on Mars.

Any estimated calculations or references on both the scenarios will be very helpful.

• when you say NRHO, do you mean the reference orbit for the Gateway station? There's a whole lot of NRHOs, and that's just one. Commented Feb 18 at 4:01
• That is correct. I am referring to the Gateway station NRHO. Commented Feb 18 at 4:28

The delta-v needed to escape from NRHO is, according to this source, almost negligible. However, performing a Hohmann transfer from Earth solar orbit to Mars solar orbit requires a burn with a delta-v of, on average, 3900 m/s.

Starship would presumably aerobrake if it were to land on Mars, but then it would need propellant to decelerate to zero and land safely - let's say that the delta-v for that is ~400 m/s. (The duration of the burn required for landing on Mars is about 40 seconds. That would be a delta-v of 392 m/s if the rate of deceleration was on average 9.8 m/s2.)

If we wanted it to enter directly into Mars orbit without aerobraking, this would require an additional burn with a delta-v of as much as 2102 m/s for a 200 km orbit.

We can use the rocket equation to work out the propellant required.

$$M_0 = M_f e^{{\Delta}V/V_E}$$

Where:

$$M_0$$ is the initial mass of the rocket,

$$M_f$$ is the mass of the rocket and payload after all burns are complete (unknown - let's assume 300,000 kg),

$${\Delta}V$$ is 3900+400 m/s or 3900+2102 m/s,

$$V_E$$ is the exhaust velocity. For a vacuum Raptor engine, this is aspirationally (3560 m/s).

Doing the math, you will need...

Objective Propellant Mass (kg)
Land on Mars 703,900
LEO Orbit 1,318,372

However, you can reduce the delta-v required for the Hohmann transfer by using an Oberth maneuver. This involves first lowering the perigee of your orbit to around 200 km above Earth's surface, and then, at perigee, executing the burn that will send your ship to Mars.

You will also need to account for propellant boil-off on the way to Mars and, if you're doing the Oberth maneuver described above, on the way to perigee. Also, if you're worried about how much time the crew will be exposed to space radiation or how long you want them to spend on Mars, you may choose a trajectory that has a higher delta-v requirement but a shorter transit time.

• A Mars Hohmann transfer requires around 3 km/s V_inf. The 388 m/s Delta_V in this answer is about what has to be added to escape velocity at 200km above earth to get that V_inf. But NRHO goes nowhere near that deep into a gravity well, so to pull this off you would first have to change from NRHO to some highly eccentric Earth centered orbit, with some cost in Delta_V. Commented Feb 20 at 10:51
• Yes, thanks for spotting that! Commented Feb 20 at 15:17