Starship―what now?

By choosing stainless steel to make Starship and its booster (=first stage), Super Heavy, SpaceX was taking a risk.  Up till now, for the most part, rockets have been made from carbon-fibre composite.  For example, SpaceX's Falcon 9 rocket, which has been remarkably successful, is of carbon-fibre.

No one knew how to make stainless steel rockets.  Steel is much heavier than carbon-fibre, though it has several advantages over it.  It can withstand much higher temperatures during re-entry, so needs a thinner and therefore lighter heat shield; it withstands the very low cryogenic temperatures of the fuel and oxidant better; it's far cheaper.  But it was all new.  When Starhopper (the first test version of Starship) was being built, YouTube and Twitter commentators thought it was a water tower! 

A couple of days ago, SpaceX launched its steel 'water tower', hovered it at 150 m, and landed it upright and safe, proving that it could be done.  So, what's next?

The next major hurdle is to land the Starship from a 20 km altitude.  To reduce speed, the Starship will use its flaps (or 'fins') in a 'skydiving' manoeuvre, falling sideways through the atmosphere, and then, at the last minute turning vertical and firing its Raptor rocket engines for the classic retro-propulsive landing we've often seen the Falcon 9 do.  We don't know whether such a manoeuvre will work.  We don't know whether the stresses applied to the long body of the spaceship by aerobrakes at each 'corner' will break it apart in the middle.  But we're going to find out, and soon.

The next critical hurdle is re-entry from orbit.  Starship will be entering Earth's atmosphere at 17,000 mph, or 27,000 kph.  The windward side will get very hot―2000 C.  Even steel will require a heat shield of ceramic tiles.  And this is a key aspect of easy re-use.  The Space Shuttle had to have each of its tiles inspected before re-flight.  If SpaceX has to do this after every flight then Starship will be far from re-usable.  However, SpaceX has already tested these tiles on a cargo Dragon capsule and they worked fine.

Then, if Starship is to go any further than LEO (low Earth orbit), for example to the Moon or Mars, it will have to refuelled in orbit.  Transferring cryogenic lox and methane between spaceships in space has never been done before.

Where are we in that testing process?

Musk has said that there will be several more 'hops', "to smooth out the launch process, then high altitude [20 km] with body flaps".    He said, in another tweet, that if the 20 km flight works, then the next test shortly thereafter will be an orbital flight.

SN8 (Serial number 8), the next Starship prototype, is ready for stacking at Boca Chica.  It will have a nosecone and functional flaps/fins, and three Raptor engines instead of just one.  It will fly to 20 kms, perhaps within a few weeks from now.  And then it will fly to LEO, if there are no problems.  Of course, there will be problems.  SpaceX's technique is to design, test to destruction, tweak the design, test again, tweak again, and so on, until it works.  I am certain we will see orbital flights of Starship before the end of this year.  

This is my latest estimate of the Mars timetable:

September 2020: Tests to 20+ kms altitude. First orbital flight of the Starship.

End 2020: Full stack (i.e., Super Heavy booster plus Starship) operational.

Early 2021: First commercial customers (for satellites), launches of Starlink constellation

Late 2022: Uncrewed mission to Mars (Mars is in opposition in December)

2023??: First commercial space station.  Launched on Starship, built by non-SpaceX companies—or maybe even by SpaceX  [Not part of SpaceX's plans]

2023: 'Dear Moon' circumlunar expedition

2024: Moon Base Alpha [Depends on NASA]

Late 2024/Early 2025: Crewed mission to Mars  (How many ships?  Here's my analysis, made before Musk revealed his planned very low cost of each Starship of $5 million. Perhaps the first uncrewed Mars Expedition could have as many as 10 ships, the first crewed 20, and the second crewed 40?)

Early 2027: Second expedition to Mars.  Return of at least one Starship.  

2029: Third expedition to Mars.  Martian population exceeds 1,000.

The important point is that we are on track for a crewed expedition to Mars by 2024, which is after all still 4 and a half years away.  At SpaceX's current rate of progress that timetable is doable.

Read Teslarati's report here.

Starship SN8 being stacked at Boca Chica
Source BocaChicaGal/Teslarati