Friday, December 11, 2015

Public-private Ceres lander

My previous post on Ceres suggested landing a batch of payloads on the surface as a proof-of-concept mission for hardware intended to explore icy moons like Europa. Let's look at the numbers.

 I will assume launch service is a single Falcon Heavy to LEO, maximum payload 53 tons at a cost of $150 million (slightly above recent prices). According to Project Rho, the dV required is 4,739m/s to make orbit and 320m/s to land.

In short, my estimate of five Europa-sized payloads seems reasonable. Costs should be in the $1.1 to $1.4 billion range, with much of the development costs applicable to the actual Europa lander and follow-on icy moon landers. In fact, I think putting a lander on every major moon of the solar system except Io could be done for less money ($10-$14 billion) than a single manned Mars landing ($20-$200 billion). Even allowing for 50% cost growth that's still around $21 billion over perhaps 20 years, not a dealbreaking increase to NASA's budget.

Full details after the jump.

Let's allow 20% mass margin. That sets our limit to 44.17 tons IMLEO.
For chemical propulsion:
 - 4,739m/s for the transfer with 10% margins would be 5,213m/s.
 - Using cryogenic propellant (LH2+LO2, exhaust velocity 4462m/s), the departure stage dry mass would be 31.09% or 13,731kg and a fuel mass of 30,436kg. (This assumes cryogenic fuel maintenance.)
 - 10% tank mass would be 3,044kg and an RL-10 or comparable engine would be 277kg. Adding in an extra 500kg for structures and mechanisms and the same for power brings us to 9,410kg of payload. This structure would serve as a Ceres orbiter and communications relay satellite to support the ground missions.
 - 320m/s for the landing with 20% margins would be 384m/s.
 - Using storable propellant (N2O2+hydrazine, exhaust velocity 3369m/s), the landing dry mass is 89.23% or 8,396kg and a fuel mass of 1,014kg. Higher-gravity bodies will require additional fuel or reduced payload.
 - 5% tank mass would be 51kg. Five R-42 DM  or comparable engines (a cluster with dual engine-out capacity) would mass 37kg. A SNAP-19 RTG (Pioneer, Viking) or comparable nuclear power source would provide about 40 watts of failsafe electrical power and about 525 watts of heat for thermal management at a cost of 15kg. Allow 500kg structures and mechanisms and 100kg power management and that brings us to 7,693kg of payload to the surface. This structure would serve as a ground observation station and possibly a communications relay.

Five 1.2-ton payloads or three 2-ton payloads could be delivered to the surface, with a further 1,693kg of science instruments split between the orbiter and lander. Given that the Curiosity rover is only 900kg, a lot of science can get done within that envelope. The lack of gravity assists or ion propulsion means the mission would proceed relatively quickly, a little over 15 months from launch to landing.
 I assume the orbiter and lander combined will cost about $500 million, a figure I consider ridiculously high but probably par for the course. Properly designed, the orbiter could be reused as a generic, modular carrier spacecraft at vastly reduced prices for future missions (in the neighborhood of $100 million).
 The same applies to the lander if it is designed to land on the majority of potential future targets; designing for a Ganymede landing with 1.2 tons of payload would be a good match to a Ceres landing with 6 tons of payload and would allow landing on the major moons of Jupiter (3), Saturn (7), Uranus (5) and Neptune (1) with the exception of Io (due to radioactive hellscape), plus other major asteroid belt objects (Vesta, Pallas, Hygiea) and Kuiper or trans-Neptunian objects (Pluto, Eris, Haumea).
 As an added risk reducer, the lander could be tested with a lunar landing payload of about 500kg. The lander would burn the same amount of fuel as for the Ceres landing and would experience similar flight and landing loads as for the highest-gravity target (Ganymede). A Falcon Heavy could place 16 tons into trans-lunar trajectory, with the lander consuming 2,220kg and roughly another 2-2.5 tons for the carrier craft. That leaves around ten tons of capacity for small satellites, telescopes, communication relays or other equipment as ride-alongs. Alternative launch vehicles could be used as well, which would serve to demonstrate a multiplatform capability for the lander and carrier components.

 Assuming we reuse the Curiosity rover design, it is still difficult to assign a cost. The overall program that resulted in that vehicle driving around on Mars was about $2.5 billion, but that is all-inclusive of development, assembly, testing, launch, ground support and future operations and includes the cost of the carrier spacecraft and the lander. The actual rover itself was likely in the $300 million range. Let's assume that after including additional development, testing and science instruments that the cost would be $450 million for an operational rover. NASA would produce one such rover for delivery. For a five-payload mission this would allow an extra 300kg of equipment, while a three-payload mission would allow a pair of full-size rovers (~$750 million in total) to count as one payload. I think this hardware could be built for much less, but better to guess high and come in under budget.

 That leaves either two or four payload slots. Other agencies like ESA or JAXA might be interested in buying a ride for their own rover. So might private entities like Planetary Resources or a new entity formed to test water extraction and delivery back to LEO. Let's assume that funding for the other payloads comes from outside sources, and that any payload slots not occupied would instead be filled with smaller payloads delivered to the vicinity of Ceres orbit rather than the surface.

 The overall mission then weighs in at $1.1 to $1.4 billion, achieving enormous savings through the re-use of existing rover and lander technology and the use of commercial launch. Up to four other entities would get a low-cost ride to Ceres, or as a fallback a large number of small payloads would be delivered to the asteroid belt. Overall a good science return for the investment. This mission would set the stage for a Europa lander and further exploration of icy moons at vastly reduced cost and risk vs. a development program that relies entirely on simulation and component testing. It would also establish a semi-standard carrier spacecraft and lander that fits within a Falcon 9H for use in future multiple-payload missions. If a lunar test mission is used, the development costs would largely apply to that mission and the Ceres mission would cost a lander, a carrier, a launch and a rover (about $650 million additional).

 The follow-on would be to deliver a proven lander to Europa. Little to no additional development would be necessary for the rover, so we can assume the same $300 million pricetag. Launch costs would be $150 million. Add a few hundred million for lander and cruise support and the mission would be around $600 million. That would put the overall program at about $1.7 to $2 billion, less payload fees from the Ceres mission. That's roughly the pricetag for the proposed Europa multiple-flyby as is, with additional costs for the Europa orbiter itself.
 Further missions with similar equipment would head for Ganymede and Callisto around Jupiter. Smaller versions or craft with more advanced propulsion might be sent as a multiple-payload mission to the moons of Saturn. This set would include the smallest known body in hydrostatic equilibrium as well as the largest known body *not* in equilibrium; a unique opportunity to make detailed observations of objects bracketing this state.
 Depending on the appetite for exploration, the lander hardware itself could become an off-the-shelf commodity part for landings on bodies up to 0.15 g and payloads of 1 to 6 tons. Ideally the rover design would be optimized somewhat for cost so that future missions would become less expensive.

No comments:

Post a Comment