The “payload” is an experiment that is at most two tanks, a valve and monitoring equipment. However it is pretty clear they will use the existing LOX main and header tanks and valves already present in every Starship. This will meet the requirements of NASA’s 2020 $53 million challenge to “transfer 10 metric tons of cryogenic propellant, specifically liquid oxygen, between tanks on a Starship vehicle”[1] as the smaller header tank holds roughly 20 tons.
If you are already attempting to get into orbit it makes sense to include this experiment in case you succeed because you save the time and cost of an entire launch and might get a $53 million award while advancing a key requirement for HLS, a $2.9 billion dollar contract and the current core mission.
This experiment has been planned for years, Starship was designed to do it and it makes sense to do it now. SpaceX clearly knows what they are doing. Unfortunately HN is terrible on this subject.
[1] https://www.nasa.gov/technology/2020-nasa-tipping-point-sele...
The big issue is that unlike all fuel that has been moved between tanks in microgravity in the past, SpaceX isn't storing their fuel in a flexible tank. Instead, they have the fuel and the pressurant gas in the same tank. Under acceleration (gravity or otherwise), this is not a problem, because the fuel pools naturally "down", with the pressurant above it.
However, as soon as the acceleration stops, there is no more down. Instead of having a bunch of fuel on the bottom and pressurant above, the tank will contain a chaotic mixture of floating gas and liquid.
The minimum setup for fuel transfer is a maneuvering system capable of a very long, weak impulse (to provide down), and then some kind of pump that moves fuel, because the force provided by the weak impulse of a maneuvering thruster is not enough to do it on it's own.
The idea of circulating a mixture & taking one you need is for example how donating blood plasma platelets works. If we can separate fuel and pressurant without too much fuss, a similar non-propulsive technique for a cryonic fill might be possible?
I'm not sure I understand how your pump idea works though.
Putting propellers on electric motors inside the tanks, to make fluid circulate axially around the center line, would propel it to intakes on the circumference, with a growing bubble running down the center. Then they would not need to accelerate the vehicle throughout the process, which alternative seems wholly impractical.
It would require clever design of the anti-slosh baffles (never shown in cutaway diagrams) to be compatible with such circulation. It might be tricky to keep the whole tank from switching to tumbling end-over-end.
"But wait, it's supposed to be more complicated than that!" No, really, they've been doing this stuff for years, and settling propellant for upper stage coasts really is virtually the same thing as settling for propellant transfer (transferring to the engine(s) for relight vs transferring to another stage... in fact you have to be MORE careful to avoid bubbles when feeding propellant to an engine than you do when transferring propellant to another tank). https://www.youtube.com/watch?v=mVAGoWJuDKk
They still need to do the whole launch-two-starships-then-dock-them bit, plus quick connect fittings, but they already have years of experience with autonomous rendezvous and docking from operating Dragon at ISS (Dragon 2 has that capability, and it has been used for the uncrewed Dragon 2 demo mission plus the recent cargo Dragon 2 missions, plus I think it's the nominal choice even for crewed missions).
In principle you could apply acceleration for a while in one direction; and then switch to accelerating in the other direction, wait for the fluid to settle at the other end, and pump from that end, alternating back and forth. But it still consumes reaction mass, and introduces delays while switching.
Docking vehicles massing hundreds of tons is a much bigger problem than docking Dragon. The Dragon experience might not apply very directly.
Presumably the engineers actually involved all understand this (literally rocket science) much better than we do.
Docking dragon is obviously similar to docking starships (Dragon berthing sensors were tested on Shuttle, broadly similar to an empty Starship). You’re right, tho, that the actual SpaceX engineers (who proposed this and developed Dragon) understand this better than random online folk.
Great attention to detail, very scientific movie.
The traditional solution is to replace acceleration/gravity with surface tension, using various types of Propellant Management Devices (PMDs).[0][1]
When last we saw our heroes, the stated plan was to solve the problem with milli-g acceleration via small thrusters.[2] That was 2017, but so far there's been no indication this part of the plan has changed.
[0] https://en.wikipedia.org/wiki/Propellant_management_device
[1] https://www.google.com/search?q=Propellant+management+device...
Literally KSP career mode IRL
building the header tanks in the first place, and testing them is the interation style. If the starship blows up, the header tanks are the least of your worries.
Are you referring to Starhopper? It is still present at Starbase as of recently.
https://www.google.com/maps/place/Starhopper/@25.9977631,-97...
Before that last flight it seemed like engine reliability wouldn't get solved. But now they have a clear path to orbit.
I doubt the heat shields will hold up on the first several re-entry attempts but there's been recent sightings of a new heat shield that has tiles about half the size. Maybe smaller tiles will have less lever action and will have 4x the fasteners.
This is still the number one problem with Starship. There were all these wild claims of an exotic new liquid cooled reentry system at the beginning. But because physics they ended up going right back to using ablative. They'll suffer the same fate as the shuttle for it. Nothing has fundamentally changed in ceramic or adhesive technology since then, and the lack of aerodynamic control means they will have to survive even steeper descents with greater thermal load. I imagine the idea of Starship as an earth return vehicle in general will probably be abandoned, so they can optimize it for interplanetary transport and lunar operations.
> the lack of aerodynamic control
There are literally wings on the ship.
Yes, it is. There is no such thing as a non-ablative reentry vehicle. The tiles are effectively no different than what was used on the shuttle.
>There are literally wings on the ship.
Starship has no meaningful aerodynamic control beyond what is required to perform the flip. It has no ailerons or elevators. It falls to the earth in a completely ballistic trajectory.
Thermal soak heat protection: the protective material absorbs - soaks - the heat, becomes really hot, and after the process need to dissipate the heat. Also - which is important - the heat capacity of the material should be enough to absorb the whole heat flux going into it. Also - thermal conductivity of this protection should be such that the protected material behind it won't get too much heat. For this kind of protection to work you want small temperature differentials - less heat flux - and small time of heating - otherwise the material will become too hot. However - as materials have varying thermal conductivity - the thermal soak is always present to some degree.
Radiative protection: the protective material heats up so much it stops accepting more heat, because it radiates heat back with the same speed. After the process the surface of this material is really hot. Important requirement - low thermal conductivity, as the high temperature on the surface shouldn't get behind the protective layer. Also known as refractory protection. Space Shuttle thermal protection is an example.
Ablative protection: the surface of the protective material releases its material in the form of gases, and this gasification process cools down the material. The material gets consumed, that's the main problem with this cooling approach - neither big thermal capacity nor small thermal conductivity are needed. Early Merlin engines used ablative cooling.
According to Wikipedia, SpaceX uses ablative protection for Crew Dragon - https://en.wikipedia.org/wiki/Atmospheric_entry#Thermal_prot... -
"A second enhanced version of PICA—called PICA-3—was developed by SpaceX during the mid-2010s. It was first flight tested on the Crew Dragon spacecraft in 2019 during the flight demonstration mission, in April 2019, and put into regular service on that spacecraft in 2020." .
Also from Wikipedia, tiles of Starship are made of silica - https://en.wikipedia.org/wiki/Starship_rocket#Starship_space... -
"Starship's heat shield, composed of eighteen thousand[131][132] hexagonal black tiles that can withstand temperatures of 1,400 °C (2,600 °F),[133][134] is designed to protect the vehicle during atmospheric entry and be used multiple times with minimal maintenance between flights.[135] The tiles are made of silica[136] and are attached with pins rather than glued,[134] with small gaps in between to allow for heat expansion.[2]"
which makes them a kind of radiative or refractory protection.
They are effectively ablative in the sense that neither vehicle has (or will) be able to complete successive missions without massive replacement of damaged and missing tiles. The fundamental approach is not suitable to reusability, as we learned with the shuttle.
The Dragon Capsule for example has an Ablative Heat-Shield. But that doesn't necessarily mean it can't do multiple missions in a row. It just depends on how the shield is designed. The Dragon could potentially do many earth missions without replacing the heat shield.
Second, you are wrong in that there is anything fundamental about Starship or Shuttle heat shield not being able to fly multiple missions. If the tiles are still attached and not damaged, then all that has to happen is for the tiles to cool down. After that they are ready for another flight, meaning the tiles are not ablative.
Now experience on Shuttle has shown that if you are not careful tiles could fall of or be damaged. Damage can be reduced in various was and Starship without an external tank is already much better by design.
Additionally Shuttle had to glue tiles to a fragile aluminum frame making the installation very hard and the tiles very fragile. Starship on the other hand uses welded studs on a steel frame. So even if a tile is lots, the steel should still hold up pretty well. In on case Shuttle was saved because there just so happened to be steel under a damaged tile.
So you are right, heat shield is one of the biggest issue that could cause problems with rapid reputability. You are wrong, the tiles are not ablative cooled. But Starship tiles are totally different then Shuttles, they have made many improvements in the heat shield and its construction and in the heat shield tiles themselves.
Starship can likely survive even with a number of missing tiles if required. In some position tile lose can certainty be fatal.
Starship will need several launches of methane+oxygen to travel beyond LEO. That model requires a reusable orbital tanker to make sense economically.
I honestly don't understand this whole post chain. The booster needs to survive because it is the most valuable part of the rocket and yet we are supposed to praise it for exploding? The hot staging concept isn't viable over the long term because it goes counter to the goals of reusability.
I don't need people to rewrite history by claiming that if the booster of the SLS exploded, it would be considered a success since nobody intends to reuse it. Yeah, that is how you get a two billion dollar launch tag. You can't convince congress to drop the SLS if you keep losing boosters.
I wouldn't praise the booster for exploding, but I would praise the engineers for getting it all the way to staging without engine failures. That's all most boosters are expected to do.
SLS isn't expected to explode because it's based on space shuttle parts that stopped exploding decades ago.
Its not that wild. That technology is likely used on certain military equipment.
I was certainty something not tested at that scale but it wasn't a crazy thing to think about.
> But because physics they ended up going right back to using ablative.
They are not ablative.
> Nothing has fundamentally changed in ceramic or
What's your evidence? Have you done lots of study on Space Heat shield? Please share your findings.
> adhesive technology since then
That just wrong. Starship uses mostly welded studs steel frame. Totally different from Shuttle.
> and the lack of aerodynamic control
They have sufficient aerodynamic control. What evidence do you have that they don't? They have shown simulation of this before. I'm gone go with SpaceX on this unless you show me some simulation that shows insufficient control.
And "time is money" - if you want to develop $ComplexTech fast, then you should start doing R&D work as soon as physically possible.
The ship is the payload. The testing is inside of the tanks of the ship. Moving fuel around inside the ship. There is no extra expensive payload in addition to the ship.