SpaceX originally planned for a number of precursor missions using Red Dragon. Now that Red Dragon has been cancelled, is there a need for something smaller before going all the way to BFR? NASA had Gemini, which was absolutely critical to the success of Apollo. On the other hand, SpaceX cancelled the Falcon 5 as unnecessary, going directly to the Falcon 9. Or, have we actually settled on the “medium” sized ship instead of ITS? That seems plausible, but now we don’t have a “small.”
The biggest problem we face without Red Dragon is characterization of Mars’ atmosphere before we send the first BFR. Red Dragon would have researched Mars’ atmospheric dynamics, to support reentry and landing algorithms. This data was considered so valuable NASA was willing to trade mission support in order to get the data SpaceX would collect. What does it mean for our architecture that this is no longer an option?
Nothing even remotely BFR-sized has ever set down on Mars. For that matter, nothing BFR-sized has ever set down anywhere. An obvious first question is how we verify the guidance algorithms for other than one gee, and how we establish that they’ll work during Mars descent?
If we assume some degree of linearity, we have an opportunity to check the guidance algorithms before heading to Mars—we can land on the Moon. If the guidance works in one gee, one atmosphere (Earth), and it also works in one-sixth gee, zero atmosphere (Moon), then that should at least boost our confidence that it will work in one-third gee, 1% atmosphere (Mars). Atmospheric dynamics is critical here, since that’s the primary mechanism BFR will use to match velocities with Mars, before igniting its engines for final landing.
Frankly, this is a little scary. In our current plan, Constellation (or Finity’s End) will arrive at Mars at the slow end of a Hohmann transfer, smash into Mars’ atmosphere to get a big delta-V, and then land on the surface under rocket power. There will be no opportunity to determine how the BFR aeroshape actually responds to Mars’ atmosphere at reentry velocities before we try it for the first time.
If Constellation succeeds, we’re fine. If either Constellation or Finity’s End fails, we have serious concerns, but we may be okay, depending on what went wrong. If both fail, for any reason, then Heart of Gold isn’t going in the next launch window. There’s no way we’ll risk a manned ship when the unmanned predecessors failed.
Without Red Dragon, do we have a way to gather data without risking a ship?
One possibility would be to send some type of BFR to Mars with no intention of landing. Instead, it would aerobrake into Mars orbit. Based on what we know about the SpaceX design, this would leave lot more room for error. In fact, if we send a fully-fueled tanker as the first ship, we buy ourselves a tremendous amount of leeway. If everything goes exactly according to plan, the end result is a tanker in orbit around Mars with a fair amount of propellant on board. If things go completely wrong, the tanker has enough propellant that it can correct for a lot of problems. Too shallow in the atmosphere, we have propellant to get us into Mars orbit from an interplanetary transfer. Too deep, we have propellant to raise the orbit to whatever degree is necessary. Either way, we now have a vehicle in orbit that can send the data it collected back to Earth.
A tanker is probably the least expensive second-stage ship SpaceX will build, so it’s a good candidate for a precursor of this type. The tanker could also provide a way to get propellant to later manned ships if everything about ISRU propellant production goes wrong. (One tanker won’t do it, but it’s still a proof of concept.)
Extending this thought a bit more, the idea of sending tankers to Mars orbit enables a variety of other options. For starters, the Lockheed Martin orbital “Mars Base Camp” suddenly seems less farfetched (https://www.lockheedmartin.com/content/dam/lockheed/data/space/photo/mbc/MBC_Updates_IAC_2017.pdf), although SpaceX tankers aren’t designed to support a hydrogen economy. Orions attached to a Mars Base Camp suddenly start to look like the orbital equivalent of rovers, able to explore Phobos and Deimos and then refuel. The Mars Base Camp itself could probably be launched fully assembled from Earth.
It could also support manned missions doing telerobotic operations. Without reusability and orbital refilling, this is borderline fantasy. With both, suddenly we exchange fully autonomous surface operations for remote control surface ops. That seems very doable. We might be able to set up water mining operations entirely from orbit. We even extend our “resupply until we get it right” concept without being stuck on the wrong end of a gravity well—with a Mars Base Camp in place (presumably supported by a MCCS), we would just need to send tankers until the manned ship has enough propellant to return.
Backing up, for the price of one tanker, we get lots of atmospheric data, an opportunity to refine our algorithms before committing to a landing, and a propellant depot in Mars orbit. It can also be done without any of the surface operations gear, autonomous deployment technology, or life support. That means it could be done before any of that is ready. Constellation and Finity’s End could launch in the next window, with much greater confidence in their ships’ handling in Mars’ atmosphere. A manned ship could even go and remain in orbit (Constellation?) to conduct telerobotic surface ops with the MFR’s cargo.
This doesn’t appear to be in SpaceX’s plan at the moment, so for planning purposes, we would need consider this a branch plan. But it seems to offer a lot of benefit. Enough, perhaps, that this branch should become the base plan.
Comment from: Member
In Musk’s 17 Sep 2018 presentation, he identified several precursor missions with tentative dates:
2019: hopper flights from Texas facility
2020: BFS high altitude tests
2020: BFR booster tests
2021 (aspirational): multiple orbital flights prior to any crewed flights
Before #dearMoon mission: probable lunar flyby, unmanned