Day: May 17, 2011

SpaceX to Mars!

This story keeps getting more interesting as I trawl around the Mars-Soc web-site. Bob Zubrin discusses the plan in more detail…

Discussion of Using SpaceX Hardware to Reach Mars

2. Technical Alternatives within the Mission Architecture

a. MAV and associated systems

In the plan described above, methane/oxygen is proposed as the propulsion system for the MAV, with all the methane brought from Earth, and all the oxygen made on Mars from the atmosphere. This method was selected over any involving hydrogen (either as feedstock for propellant manufacture or as propellant itself) as it eliminates the need to transport cryogenic hydrogen from Earth or store it on the Martian surface, or the need to mine Martian soil for water. If terrestrial hydrogen can be transported to make the methane, about 1.9 tons of landed mass could be saved. Transporting methane was chosen over a system using kerosene/oxygen for Mars ascent, with kerosene coming from Earth and oxygen from Mars because methane offers higher performance (Isp 375 s vs. Isp 350 s) than kerosene, and its selection makes the system more evolvable, as once Martian water does become available, methane can be readily manufactured on Mars, saving 2.6 tons of landed mass per mission compared to transporting methane, or about 3 tons per mission compared to transporting kerosene. That said, the choice of using kersosene/oxygen for Mars ascent instead of methane oxygen is feasible within the limits of the mass delivery capabilities of the systems under discussion. It thus represents a viable alternative option, reducing development costs, albeit with reduced payload capability and evolvability.

b. ERV and associated systems.

A kerosene/oxygen system is suggested for Trans-Earth injection. A methane/oxygen system would offer increased capability if it were available. The performance improvement is modest, however, as the required delta-V for TEI from a highly elliptical orbit around Mars is only 1.5 km/s. Hydrogen/oxygen is rejected for TEI in order to avoid the need for long duration storage of hydrogen. The 14 ton Mars orbital insertion mass estimate is based on the assumption of the use of an auxiliary aerobrake with a mass of 2 tons to accomplish the bulk of braking delta-V. If the system can be configured so that that Dragon’s own aerobrake can play a role in this maneuver, this delivered mass could be increased. If it is decided that the ~1 km/s delta-V required for minimal Mars orbit capture needs to be done via rocket propulsion, this mass could be reduced to as little as 12 tons (assuming kerosene/oxygen propulsion). This would still be enough to enable the mission. The orbit employed by the ERV is a loosely bound 250 km by 1 sol orbit. This minimizes the delta-V for orbital capture and departure, while maintaining the ERV in a synchronous relationship to the landing site. Habitable volume on the ERV can be greatly expanded by using an auxiliary inflatable cabin, as discussed in the Appendix.

c. The hab craft.

The Dragon is chosen for the primary hab and ERV vehicle because it is available. It is not ideal. Habitation space of the Dragon alone after landing appears to be about 80 square feet, somewhat smaller than the 100 square feet of a small standard Tokyo apartment. Additional habitation space and substantial mission logistics backup could be provided by landing an additional Dragon at the landing site in advance, loaded with extra supplies and equipment. Solar flare protection can be provided on the way out by proper placement of provisions, or by the use of a personal water-filled solar flare protection “sleeping bag.” For concepts for using inflatables to greatly expand living space during flight and/or after landing, see note in Appendix.

…which gratifyingly echoes my own thoughts. Landing a Dragon directly on Mars has a great appeal and as a Mars Descent Vehicle it’s a good system, given the modifications Zubrin outlines. But is it a Mars Habitat? The Inflatable extensions make it viable and I was wondering if Bigelow, SpaceX and Mars-Soc couldn’t combine forces on a design. Zubrin argues for eventual extensions of the architecture itself, calling for eventual Heavy Lift systems able to throw 30 tonnes to Mars, but IMO the Falcon Heavy Tanker modification is sufficient to launch ~24.7 tonne payloads now and with an LH2/LOX Stage II it might easily launch ~30-40 tonnes. Alternatively two FHTs can be ganged to launch 55-60 tonnes directly now. However such modifications are deployed is perhaps irrelevant. What’s needed is the political will to commit to Mars Colonization, not just a one-off stunt. All the good ideas to improve how we get there are irrelevant until we actually do…

SpaceX to Mars?

SpaceX has answered the skeptics recently with a frank discussion of its costs thus far in its May 4, 2011 Update. An excerpt of relevance is this…

WHY THE US CAN BEAT CHINA: THE FACTS ABOUT SPACEX COSTS

The Falcon 9 launch vehicle was developed from a blank sheet to first launch in four and half years for just over $300 million. The Falcon 9 is an EELV class vehicle that generates roughly one million pounds of thrust (four times the maximum thrust of a Boeing 747) and carries more payload to orbit than a Delta IV Medium.

The Dragon spacecraft was developed from a blank sheet to the first demonstration flight in just over four years for about $300 million. Last year, SpaceX became the first private company, in partnership with NASA, to successfully orbit and recover a spacecraft. The spacecraft and the Falcon 9 rocket that carried it were designed, manufactured and launched by American workers for an American company. The Falcon 9/Dragon system, with the addition of a launch escape system, seats and upgraded life support, can carry seven astronauts to orbit, more than double the capacity of the Russian Soyuz, but at less than a third of the price per seat.

Note the cost of developing the “Dragon” which is the first private aerospace vehicle proven capable of return from orbit. About $300 million, with a dry mass of about ~4.2 tons, thus ~$72 million/ton to develop. To develop large Mars mission vehicles might be assumed to cost similar amounts per ton of aerospace machinery. But can it be done even cheaper?

The Mars Society has made an impassioned plea to President Obama to consider a minimalistic Mars Mission concept based on the Falcon Heavy and Dragon space-vehicle…

The SpaceX’s Falcon-9 Heavy rocket will have a launch capacity of 53 metric tons to low Earth orbit. This means that if a conventional hydrogen-oxygen chemical rocket upper stage were added, it would have the capability of sending 17.5 tons on a trajectory to Mars, placing 14 tons in Mars orbit, or landing 11 tons on the Martian surface.

The company has also developed and is in the process of demonstrating a crew capsule, known as the Dragon, which has a mass of about eight tons. While its current intended mission is to ferry up to seven astronauts to the International Space Station, the Dragon’s heat shield system is capable of withstanding re-entry from interplanetary trajectories, not just from Earth orbit. It’s rather small for an interplanetary spaceship, but it is designed for multiyear life, and it should be spacious enough for a crew of two astronauts who have the right stuff.

Thus a Mars mission could be accomplished utilizing three Falcon-9 Heavy launches. One would deliver to Mars orbit an unmanned Dragon capsule with a kerosene/oxygen chemical rocket stage of sufficient power to drive it back to Earth. This is the Earth Return Vehicle.

A second launch will deliver to the Martian surface an 11-ton payload consisting of a two-ton Mars Ascent Vehicle employing a single methane/oxygen rocket propulsion stage, a small automated chemical reactor system, three tons of surface exploration gear, and a 10-kilowatt power supply, which could be either nuclear or solar.

The Mars Ascent Vehicle would carry 2.6 tons of methane in its propellant tanks, but not the nine tons of liquid oxygen required to burn it. Instead, the oxygen could be made over a 500-day period by using the chemical reactor to break down the carbon dioxide that composes 95% of the Martian atmosphere.

Using technology to generate oxygen rather than transporting it saves a great deal of mass. It also provides copious power and unlimited oxygen to the crew once they arrive.

Once these elements are in place, the third launch would occur, which would send a Dragon capsule with a crew of two astronauts on a direct trajectory to Mars. The capsule would carry 2500 kilograms of consumables—sufficient, if water and oxygen recycling systems are employed, to support the two-person crew for up to three years. Given the available payload capacity, a light ground vehicle and several hundred kilograms of science instruments could be taken along as well.

The crew would reach Mars in six months and land their Dragon capsule near the Mars Ascent Vehicle. They would spend the next year and a half exploring.

Using their ground vehicle for mobility and the Dragon as their home and laboratory, they could search the Martian surface for fossil evidence of past life that may have existed in the past when the Red Planet featured standing bodies of liquid water. They also could set up drilling rigs to bring up samples of subsurface water, within which native microbial life may yet persist to this day. If they find either, it will prove that life is not unique to the Earth, answering a question that thinking men and women have wondered upon for millennia.

At the end of their 18-month surface stay, the crew would transfer to the Mars Ascent Vehicle, take off, and rendezvous with the Earth Return Vehicle in orbit. This craft would then take them on a six-month flight back to Earth, whereupon it would enter the atmosphere and splash down to an ocean landing.

Spending ~2.5 years in a Dragon capsule will take a couple of claustrophiles, but people have endured in remarkably nasty conditions. So why not? It’s daring, but is it necessary?

Zubrin asks for a cryogenic upper-stage to throw the Mars vehicles to Mars, but is that really needed? Can better performance be achieved by using a slightly different approach? In a previous post I outlined the Falcon Heavy Tanker (FHT) – essentially a Falcon Heavy Stage 2 with a stretched tank and a docking collar for coupling to a Dragon. I estimated 55 tonnes of RP-1/LOX could be placed in orbit and a FHT dry-mass of 2.5 tonnes. To get to Mars takes ~3.7 km/s from LEO, the so-called Trans-Mars Insertion (TMI) delta-vee, thus with a vacuum Isp = 342s, that means the Falcon Heavy Tanker can push 27.2 tonnes into a TMI orbit, thus a net payload of ~24.7 tonnes. With aerobraking that’s considerably more than the Mars Society’s quoted payloads, providing somewhat better living conditions for the explorers.

Of course the payloads need to be orbitted separate to the FHTs, but at less than half the Falcon Heavy’s usual 53 tonne payload, that means 2 separate Mars payloads can be orbitted by one vehicle, and supported by a separately orbitted crew in a Dragon. Potentially we can reduce the FHTs to just three to support a beefier Mars Semi-Direct mission which doesn’t mean living in a Dragon capsule for 2.5 years! Alternatively we launch the Mars Ascent Vehicle directly via a single Falcon Heavy, as per the Mars Society plan, and launch the Mars-bound Habitat and Earth Return Vehicles via 2 FHT launches and 1 Falcon Heavy. Four Falcon Heavy launches versus 3, but delivering more payload.

Zubrin is, I suspect, hoping to minimize the cost of developing new systems, thus using two Dragons and only needing to develop a low-mass Mars Ascent Vehicle. However the current Dragon probably can’t be used as a Habitat for +2 years with some development work, thus the difference between the two approaches is probably negligible. I appreciate his gumption and burning desire to get a finger-hold on Mars as soon as possible, but I’d like to see the developed systems able to do more than a stunt.

Go SpaceX! Go Mars-Soc!