Zubrin's take on Elon's Mars plans

Elon Musk has revealed his true nature over the last year.  I used to admire him, believing that he wished to make the world a better place.   I no longer think that.  Nevertheless,  I am going to continue to report news and opinions about SpaceX's Starship,  as I have been a keen follower since it was first announced nearly ten years ago, and because I believe that mankind should go to Mars.

Starship remains far ahead of any competitor.  There's the DreamChaser, but it's been in development for 20 years, and its first lauch has just been postponed again.  Jeff Bezos's New Glen reusable booster has only just had one launch, which wasn't completely successful.  Unlike SpaceX, which has landed its booster, and will soon land Starship, New Glen has yet to return safely to base.

Starship had its first successful flight two days ago, after several failures.  SpaceX's development method is to test its rockets in action, see what's wrong, fix the issues, and then test again.  It's taken 10 Starship launches to get its first success, and there is still a long way to go.  Reusable rockets are essential, to cut costs, and for Starship, that means getting the heatshield tiles to work.  Perhaps another 10 launches will be needed for the technical problems with the heatshield to be solved.  A first step will be to launch Starship and let it land at Starbase, rather than into the sea, so that the engineers can see what's wrong by inspecting the damage to the tiles, the hull and the fins.

Despite the technical difficulties, I have no doubt that Starship will over the next couple of years become as reliable a workhorse as the Falcon 9.  But will it be the foundation for a Mars city?  Well, probably not.  

I've talked before about Zubrin's plans.  He points out that there are no great grasslands or oceans on Mars, and that we can't colonise it in the same way the New World was colonised.  We will have to grow all our food inside domes or caverns.  The initial populations on Mars will be limited by this.  He also argues that a "Starboat" (a rendering is shown below), about 1/5th the size of the Starship, would be much more practical, because the energy needs to produce propellant for Starship for the return journey to Earth would require 60,000 square metres of solar panels, which by themselves would need 3 Starships, and therefore another +-20 launches of refuelling tankers.  A Starboat would require only 1/5 of that.  In addition, a "Starboat" could be lifted  fully fuelled from Earth into orbit by a Starship, ready to head to Mars, and would not require in-orbit propellant transfer.

Musk is fixated on having just one workhorse: Starship.  Yet it has already morphed into 4 distinct variants:  the passenger Starship; the fuel tanker; the cargo version with its huge bay door; and the Moon landing vehicle.  One more wouldn't make much difference.

A concept for "Starboat"

Here is a video about Robert Zubrin's take on Musk' Mars plan.

Will we get to Mars?  Yes.  Will Mars have a million inhabitants by 2060?  I doubt it.  

But the first scientific bases will expand, and eventually there will be small towns with a few thousand inhabitants living in domes and caverns.  It will take decades to reach a Martian population of a million.

Meanwhile, the need to make it all work will be powerful technological driver, providing incentives to develop the technology needed for a space civilisation, all of which will be good for Earth.  Think for example of the need for vat meat and fish, for air and water purification systems, for workable, safe, small nuclear reactors, for plant varieties which can flourish in very different conditions from on Earth, and for more efficient, cheaper and faster transportation between Mars and Earth.  Just as space has already led to incredibly useful new technologies on Earth--solar panels being just one--so will Mars lead to improvements in Earth-based technology and science.

Musk's comments on in-orbit refuelling of Starship

Starship continues to develop, and its design just keeps on being tweaked.  For flights to the Moon or to Mars, Starship will have to be refuelled in orbit.  When Starship (then the BFR) was first mooted by SpaceX decades ago, refuelling was going to be "belly-to-belly" as it were, with the tanker lying adjacent to the Starship to refuel.  Actually, that "decades ago" is just a dig at SLS, NASA's incredibly expensive and horribly delayed rocket which is supposed to get us to the Moon.  In fact, SpaceX started development of Starship, then called BFR, just 5 years ago, in 2016.  After the initial plans, SpaceX then switched to what is inelegantly described as "butt-to-butt" fuel transfers.  But experience has shown that this is too dangerous, with extraneous fuel lines next to rocket engines just too unsafe.  So we're back to "belly-to-belly" refuelling.

This all came out when Blue Origin, Jeff Bezos's pet project, chucked a wobbly about SpaceX being awarded  part of the Artemis Moon landing project.   This report is from Teslarati.

After a much-anticipated GAO denial of Blue Origin and Dynetics protests over NASA’s decision to solely award SpaceX a contract to turn Starship into a crewed Moon lander, an in-depth (but heavily redacted) document explaining that decision was released on August 10th.

Aside from ruthlessly tearing both companies’ protests limb from limb, the US Government Accountability Office’s decision also offered a surprising amount of insight into SpaceX’s HLS Starship proposal. One of those details in particular seemed to strike an irrational nerve in the online spaceflight community. Specifically, in its decision, GAO happened to reveal that SpaceX had proposed a mission profile that would require as many as 16 launches to fully fuel a Starship Lander and stage the spacecraft in an unusual lunar orbit.

After around 24 hours of chaos, confusion, and misplaced panic, SpaceX CEO Elon Musk finally weighed in on the GAO document’s moderately surprising indication that each Starship Moon landing would require sixteen SpaceX launches.

Confirming many expectations, SpaceX’s solution to sending an entire single-stage Starship to the Moon, landing it on the lunar surface, and returning it to a lunar orbit (and maybe even Earth) goes as follows.

First, SpaceX will launch a custom variant of Starship that was redacted in the GAO decision document but confirmed by NASA to be a propellant storage (or depot) ship last year. Second, after the depot Starship is in a stable orbit, SpaceX’s NASA HLS proposal reportedly states that the company would begin a series of 14 tanker launches spread over almost six months – each of which would dock with the depot and gradually fill its tanks.

Third, once the depot ship is topped off, the actual Starship Moon lander would launch, dock with the depot, and be fully fueled. Finally, the fueled lander would fire up its Raptor engines and head to the Moon, where it would enter a near-rectilinear halo orbit (NRHO) – a weird high-altitude, elliptical orbit only necessary because NASA’s Orion spacecraft and SLS rocket are too underpowered to reach a more normal, functional orbit around the Moon.

After reaching NRHO, Starship would dock with Orion (or vice versa), receive its Artemis astronauts, land on the Moon for several days, and launch back to NRHO to return those astronauts to Orion. After its main mission is complete, it remains to be seen if Starship will have enough propellant left over to return to some kind of Earth orbit, where it could potentially be refueled and reused on future missions to the lunar surface.

In response to GAO revealing that SpaceX proposed as many as 16 launches – including 14 refuelings – spaced ~12 days apart for every Starship Moon lander mission, Musk says that a need for “16 flights is extremely unlikely.” Instead, assuming each Starship tanker is able to deliver a full 150 tons of payload (propellant) into orbit after a few years of design maturation, Musk believes that it’s unlikely to take more than eight tanker launches to refuel the depot ship – or a total of ten launches including the depot and lander. 

[Musk added, in a tweet (how else): 

"Without flaps & heat shield, Starship is much lighter. Lunar landing legs don’t add much (1/6 gravity). May only need 1/2 full, ie 4 tanker flights.  However, even if it were 16 flights with docking, this is not a problem. SpaceX did more than 16 orbital flights in first half of 2021 & has docked with Station (much harder than docking with our own ship) over 20 times."]

But, as Musk notes, so long as Starship gets anywhere close to its design objectives, it would be a non-issue even if each Starship Moon lander mission somehow required 16 launches. A step further, assuming that SpaceX proposed 16 launches per mission out of an abundance of conservatism, it’s fair to assume that a 12-day gap between tanker launches is also an extremely conservative worst-case scenario. Per Musk and SpaceX, Starship’s design goals call for multiple reuses of ships and boosters per day. Even if SpaceX falls a full magnitude short of those ambitious goals, Starship tankers should feasibly be able to launch every few days or maybe every week.

But thanks to SpaceX’s relatively conservative proposal, the company now knows that NASA is more than happy with Starship even if it falls something like 50% short of its payload performance goals and two magnitudes short of its reusability goals.

 

Starship refuelling in orbit.
Render by Erc X

As an aide-mémoire, here is my Mars timetable.

Astroclipper spaceplane

Earth's gravity well is too deep for single-stage-to-orbit spacecraft.  For example, though SpaceX's Starship would make it to orbit, it would have no fuel to return, let alone be able to carry a payload.  So we need two stages to lift a payload into orbit, and to make launches and space travel cheap (relatively), each stage needs to be re-usable.   SpaceX has done this already, with its Falcon 9 and Falcon Heavy, though Crew Dragon, the re-usable capsule to take crew to the ISS  (International Space Station) hasn't yet flown, and suffered a nasty setback when a previous prototype blew up during testing.  SpaceX's Starship/Super Heavy duo hasn't yet flown, though early tests have been promising.  If Starship/Super Heavy works it will be able to lift 100-150 tonnes into LEO (low Earth orbit) at 1000th the cost of existing launch systems.  But SpaceX's rockets lift off and land vertically, and that is on purpose—Starship is designed to work on celestial bodies where there is no atmosphere, such as the Moon.  Since the earliest days of space travel, the dream has been to have space vehicles which can take off from and land at airports just like planes.

Fraser Cain has done a good video about Astroclipper, a combined plane/rocket, which will do just that.

(All images from Fraser Cain's video)

The X-33, a single-stage-to orbit spaceship which was planned by NASA and then cancelled.  It would take off vertically then coast to a landing like an aircraft.  A 1/3rd size mockup was built, but the project was then cancelled.

But a winged spaceship (to assist re-entry and re-use) was first planned in 1957, and was called the Dynasoar.  It too was cancelled, for budgetary reasons.  This is the wind tunnel test model.

NASA toyed with this version of a re-usable booster, which would take off from an airport (instead of vertically) and then land at an airport.

Exodus Space Corp's solution is a two stage spaceplane.  It takes off from an airport like a jet, using conventional air-breathing jets.  At about 20 kilometres altitude, the rocket engines take over.  In an interesting wrinkle, the oxidiser isn't liquid oxygen (which means cryogenic fuel tanks with all their problems) but hydrogen peroxide.  At 75 to 110 k's, the two stages separate, and the first stage coasts back to land at an airport.

This is the timeline which Exodus Space Corp suggests.  The competitive advantages they point to seem plausible.  The timeline does not. 

The thing is, there is a ferment of new developments in space exploration right now.  SpaceX plans to have commercial launches of Starship by mid 2021, Blue Origin's New Glenn will have commercial launches in 2022, and Sierra Nevada Corporation's Dream Chaser in 2021.  By the mid 2030s, competing technologies will have gone through a couple of iterations.  Exodus Space Corp's offering will be competing against seasoned and familiar technology which will be hard to beat.  Given how rapidly SpaceX is developing its technologies, it's hard to see that they won't see off this competition.  If this two-stage spaceplane is cheap and convenient enough, SpaceX or Blue Origin or Virgin Space will easily be able to copy what Exodus Space Corporation is doing, because these ideas can't be patent-protected, and all the other players will be able to diversify from their existing technologies to produce something comparable.

Extremely interesting, all the same.

Dreamchaser

This is a space shuttle which looks like the former NASA Space Shuttle, except it's a lot smaller.  Unlike SpaceX's BFR/BFS/Starship/Super Heavy, it's designed purely to get to and from LEO.  Like the Shuttle, it will glide in to land at airport runways, whereas SpaceX's and Blue Origin's plans call for retro-propulsion (firing rockets to slow the booster or capsule for landing)

Initially, it'll just be for cargo, but later on, plans are that a crew version will be able to carry people (5, I think) to and from ISS.  NASA has approved its production, and has given Sierra Nevada Corporation, the company building DreamChaser (where did they get that name?) a contract for 6 missions to the ISS.

Competition is good.  It leads to lower costs and new ideas, especially where technology is developing rapidly.  The legacy space companies (ULA, Boeing, Lockheed Martin, ESA, Roscomos) are all expensive.  The newcomers (Sierra Nevada, SpaceX, Blue Origin, Virgin Galactic) are all pursuing different pathways to getting us into space cheaply.   One thing they all have in common, though, is re-usability.  That is key to cheap space.  SNC says that launch vehicle costs with ULA, which doesn't do re-usable, are 80% of the cost of every mission they fly.  If they switch to SpaceX or Blue Origin, those costs will fall 10-fold.