Day 9 - Sequencing the Missions
If we assume the plan as announced by SpaceX (at least for now), what does this mean for the follow-on mission architecture? At the next (third) launch window, two resupply ships brings more of everything… food, equipment to build out the base, additional solar panels, rovers, parts for the ISRU plants, spare oxygenators, spare spacesuits… and 16 more people. We had 12 people on-planet, with life support for 24. With this mission, our goal is to increase life support capacity, power, everything. We’ll assume a MCCS and an MFR.
Once we have a manned ship on Mars, we’re making propellant for a return trip. An early goal is to get Constellation and Finity’s End heading back to Earth at the first available Mars-Earth return window.
This is a sequencing issue. Launch windows to Mars open every 26 months—about every 790 days. With a 180 day travel time from Earth to Mars, the Earth-return window for a “conjunction” class trajectory (180 days back to Earth) opens 550 days after arrival…730 days into the mission. The first time this occurs, Heart of Gold and Nostromo haven’t even left Earth yet. Heart of Gold won’t launch until Constellation’s 790 mission day point, takes 180 days en route, and arrives Mars at the 970 mission day point. There are 240 days between the return window and the arrival of the follow-on ship.
That’s a potential problem for the other COA’s, because those 240 days represent time when the base could be left unmanned. We don’t have that problem here. Instead, Constellation and Finity’s End wait on Mars until the next conjunction-class Earth return window opens, 550 days after Heart of Gold and Nostromo arrive. Doing math the easy way, this means the unmanned ships depart for Earth at their 1520 mission day point, arriving back on Earth at 1700 days mission-elapsed-time.
This also means we have 550 days after Heart of Gold and Nostromo arrive to manufacture enough propellant to get Constellation and Finity’s End heading back to Earth. That’s 18 months. As a first pass, this seems reasonable. If it turns out we’ve been overly optimistic, we could send only Finity’s End. This repositions a ship that can bring us more supplies, and leaves the spare life support capability in place.
Let’s reiterate: Constellation and Finity’s End land on Mars, and skip their “first return” opportunity. Heart of Gold and Nostromo land next, and start making propellant to let Constellation and Finity’s End go home at their second return opportunity.
Implicit in this plan is that Heart of Gold does not go home at its first return opportunity—that’s the window when Constellation and Finity’s End return to Earth. If Heart of Gold also left, the base would be left unmanned for 240 days, while waiting for the third MCCS to arrive. We don’t want that.
So, now we need another MCCS, presumably another MFR, two more names, and a sequence for this architecture.