Trans Mars Injection

john hare


Rand Simberg (Transterrestrial Musings)posted a few concepts for mars missions the other day involving refueling at various interplanetary depots with attendant advantages. Unfortunately, I couldn’t quite grasp the advantages compared to other depot scenarios in more  conventional orbits. Though I am not a Mars first advocate, a lot of people are, and Mars is certainly going to be a relatively high traffic interplanetary destination for the foreseeable future. So I though I would try to figure out a most bang for the buck  concept for a high mass Mars mission. It’s not all my ideas, just the best arrangement I could conceive shooting from the hip.


Rand suggested four Falcon IXH launches for the mission. I think that’s a good start. Four Falcon IX heavy launches totals 212 metric tons in LEO. IMO the challenge is to get as much of that as possible into TMI. Methods of rendezvous with Mars on the other end and the goals of that mission are up to you.

Launch three Falcon IXH into LEO well ahead of the Mars launch window. Use electric propulsion to send all three of them to an eccentric lunar orbit at just under lunar escape velocity with a  perelune just high enough to be safe. The fifty three tons each in LEO should result in a total of about a hundred and forty three metric tons in that orbit assuming they expend no more than ten percent of their initial mass for the trip with the high efficiency (Isp) electric propulsion. Dock the three ships together.

Launch the fourth Falcon IXH with crew as the Mars launch window opens. In LEO, detach the five ton inspace crew taxi with ten tons of kero/LOX propellant from the rest of the ship and send it on a normal four day lunar insertion trip. The other thirty eight tons of Falcon IXH payload follows slowly on electric propulsion. The taxi mates with the first three vehicles in eccentric lunar orbit to create a single manned TMI vehicle of a hundred and forty eight tons.

The TMI vehicle makes a few meter per second burn to kick it out of lunar orbit into an Earth grazing trajectory. At peregee the kero/LOX engine fires for a roughly three hundred meter per second Oberth effect burn to put the whole vehicle on a Trans Mars Injection orbit. This should put a manned vehicle of about a hundred and thirty four tons into the TMI. This vehicle has both the kero/LOX high impulse engines from the taxi, and the high efficiency electric propulsion from the first three Falcon IXH vehicles for a mixed propulsion availability considerably better than either alone. When the thirty four tons remaining of the fourth launch catches up, the total vehicle will be one hundred and sixty eight tons heading for Mars.

It will be interesting to see if this is feasible, and how it compares to other scenerios involving four Falcon IXH launches with or without depots.



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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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4 Responses to Trans Mars Injection

  1. Andrew Swallow says:

    For a manned mission a return journey is needed.

    ISRU carbon monoxide, methane and LOX could be made.

  2. john hare says:

    Most options ever considered for a first manned mission could be done with that 168 tons on TMI.

    It is not absolutely true that a return must be part of each mission plan. It is possible that the first mission would stay on the ground doing useful work until relieved by the crew of the next launch window. That would give something over two and a half years of boots on the ground per crew.

    It is also possible to do Flags and Footprints or One Way To Stay within this mass budget. As I said in the post, methods of rendezvous and goals of the mission on the other end are up to you.

  3. Andrew W says:

    What you describe is what I’d expect to obtain the highest TMI mass, the only suggestion I’d add is to launch the propellant from Earth in the form of water and spend the time in eccentric lunar orbit using the electric generation system (whatever form it takes) converting the water to LOX/LH2, so you need less high gravity tank volume.

  4. john hare says:

    I was assuming that only the four Falcon IXH launches would be available. If somebody is already doing depots though, they would certainly be happier to sell higher impulse propellants for a premium as you imply. Keep the Falcon IXH upper stages attached and purchase propellant to fill them up in LEO and again in eccentric lunar orbit. No electric or other exotic propulsion needed for the mission itself. After the 300 mps TMI burn at perigee, there would be 212 metric tons of vehicles headed for Mars with a few km/sec of propellant in the tanks which would also be useful for shielding. Total vehicle including propellant in TMI on the order of 500 metric tons.

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