Many of the answers are in videos that I've done in the past. You can find past videos by going to eagerspace.net and searching around.
Onto the questions
3: How do you see Chinas private space sector in the coming years? They seem to be making fairly rapid progress given their lack of foundational knowledge. I think we could see a Falcon 9 style vehicle in a few years.
I get asked that often and I don't have enough interest or context to give a real answer.
I linked to a few people who know a lot more near the end of this video.
4: Do you think blue origin will beat SpaceX to the moon?
Two years ago I would have said "definitely not".
Today I would say "unlikely".
Starship is definitely in a bad state but SpaceX has a lot of money, a lot of experience, and a big team.
Blue Origin is still working hard to fly New Glenn more than once.
I'll also note that the lunar lander contracts aren't like crew or cargo resupply for ISS, where there were two companies competing to see who was first. SpaceX *has* the sole contract for Artemis 3 and 4 right now, and it's not clear if NASA can change that even if Blue Moon is ready earlier.
5: Rocket Lab has mentioned the possibility of a crew capsule, but with the hungry hippo fairing and enclosed upper stage of Neutron, how do you expect them to design for crewed flights vs regular launches?
Here's something that I found pretty surprising...
You can fit a crew dragon inside a Neutron second stage if you can fix the small issue of the fins on the trunk, so I think that there's no reason you can't put a capsule inside the current design.
For abort you just blow the fairings off and then trigger the abort engines in the capsule.
6: How did they make the Soyuz spacecraft so lightweight compared to others crewed spacecraft?
Interesting question. Let's look at some capsules.
The workhouse Russian Soyuz consists of 3 modules. The crew rides in the descent module on both launch and descent, the orbital module gives them more space when they are in orbit, and the service module at the bottom provides power, engines, etc. The descent module is the only part that returns intact.
The Chinese Shenzhou (shen-joe) capsule uses the same layout as the Soyuz - it's almost like the Chinese adopted the Russian design - but it is slightly upsized, with about a 25% larger diameter.
The US and European Orion capsule skips the orbital module but is much larger than the others.
And finally, the Crew Dragon looks like it has a service module, but the rear section is the hollow trunk. It exists modifies the aerodynamics of the capsule so it flies forward in abort scenarios, provides a location for the solar panels and radiators, and the internal volume can be used to carry large cargo.
The Soyuz launch mass is 7.1 tons and 3 tons of that returns.
The Shenzhou launch mass is 7.8 tons and 3.2 tons of that returns.
The Orion is a beast, with the capsule massing 10.4 tons by itself and the service module massing 15.5 tons, for a total of 25.9 tons. It's intended to be a capsule that astronauts can stay in for the long lunar missions and the service module has enough propellant to get into and out of lunar orbit. It's still very portly.
Crew Dragon has a total mass of 12.5 tons but returns 9.6 tons to the ground.
7: How did they make the Soyuz spacecraft so lightweight compared to others crewed spacecraft?
Now let's look inside.
The Soyuz carries a crew of 3 but has only 3.5 cubic meters of volume.
Astronaut Don Pettit said (read)
Astronaut Doug Wheelock said (read)
It's bad enough that the crew sometimes takes pain relievers before the flight to help deal with the muscle cramps that result from the position.
Pictures of both outside appropriately scaled, then pictures of inside versus crew dragon.
8: How did they make the Soyuz spacecraft so lightweight compared to others crewed spacecraft?
The Shenzhou capsule also carries three, but it's much larger at 6 cubic meters. You can see that there is considerably more space than Soyuz.
9: How did they make the Soyuz spacecraft so lightweight compared to others crewed spacecraft?
Orion is designed to carry up to 6 crew but is currently only planned to fly with 4. It provides normal seating arrangements, though the two-row arrangement means some crew members have feet over the heads, and a palatial 8.9 cubic meters of volume.
10: How did they make the Soyuz spacecraft so lightweight compared to others crewed spacecraft?
And finally, Crew Dragon is sized to carry up to 7 but normally carries only 4, and it has 9.3 cubic meters of habitable volume.
Discounting Orion - which is really doing a very different job - crew dragon is bigger and heavier for two reasons.
The first is that it is designed for a larger crew, and the second is that it is reusable and brings the bulk of the launch mass back to the ground. More mass coming back requires a heavier and more robust heat shield.
11: How did they make the Soyuz spacecraft so lightweight compared to others crewed spacecraft?
Interesting question.
Pictures of both outside appropriately scaled, then pictures of inside versus crew dragon.
12: What rate of power production is needed (from solar, nuclear, whatever) to re-fill Starship's oxygen tank with ISRU oxygen from the lunar surface in a "reasonable" amount of time?
This is a good one to say that the answer is left as an exercise for the student...
I will tell you that it takes somewhere between 150 and 800 kilowatt hours to liquify a ton of oxygen. If you are thinking about getting the oxygen from regolith, this paper might be helpful.
If you are looking to get it from lunar water, there are other papers that discuss that.
13: I've wondered for a while now if Stirling engines would be great at generating electricity in space with temperatures in the sun being extremely hot and in the shade extremely cold. Do you know if that sort of power solution has been studied?
It turns out that neither of those things are true.
The sun puts out about 1500 watts (check) of power per square meter, so to get a bunch of power you need a lot of space to absorb sunlight.
But the only way to get rid of heat in space is to use radiators, and they are not very good at that for low temperatures.
That's why the relatively small kilopower reactors that NASA is designing for lunar use have really big radiators.
14: Why won't spacex develop a disposable upper stage for super heavy
They have.
Just like there's a disposable Falcon 9 without grid fins or landing legs, take starship and get rid of the fins and all the heat shield tiles and you have a disposable Starship.
15: Musk's current Mars plan has astronauts landing on mars as early as 2028. The thing I haven't seen him or any other companies discuss is radiation protection.
Here are a couple of papers of interest
16: My biggest gripe and question is why we still use Specific Impulse. Like I get the whole "easy to translate between units" but it is horribly unintuitive for me.
The root value for specific impulse is exhaust velocity, and I think that is somewhat intuitive from a physics perspective - the faster you can throw a given amount of mass out the back the more thrust you get.
I personally don't find any of the explanations for the units of specific impulse to be useful. I just treat it as a dimensionless measure of propellant economy.
17: Do you think Space X will make the world's first space dock( where a craft is built in space only to live in space and never land on Earth.)? When will this happen in your guess?
18: Do you think starlink and similar systems provide a genuine benefit to humanity that extends beyond providing competition to particularly greedy internet companies in rich countries, or giving scientists in remote places opportunity to scroll social media?
Yes.
Estimates for how many people do not have internet access range from 2.5 billion to 2.9 billion, or about 35% of the world's population.
19: In the long run, which is better a reusable launch vehicle that only flies occasionally or a mass produced expendable rocket that is launched frequently
I'm not sure I really understand the options - it's not clear to my why the reusable rocket would only be launch occasionally but the expendable would be launched often.
If Starship versus Vulcan is an example, then those are two very different rockets.
20: Do you think SpaceX would have failed if not for some lucky timing and appallingly bad decisions/performance by established competitors?
Absolutely. Here's a video for you.
21: Any interest is exploring EU or Russian space industry? I know you are not interested in the Chinese launch industry but is that the same with all non American industries
I talked about the EU a little in my 2025 launch company analysis. The challenge with the EU is that the new companies would like to work with the ESA but the ESA is a weird organization that works across companies.
Russia is really hard because I try to do my analysis based on what has been done rather than what has been promised, and Russia isn't doing much right now and they are promising some things that are hard to believe.
22: 1 - As an alternative to SLS could a disposable Starship be used to launch Orion to the moon without any refueling?
23: 8 - Do you think congress will create a new launcher for NASA after they are unable to justify SLS? And what do you believe they could justify
Congress has never felt the need to justify SLS and I'm not sure they would change that post SLS.
The space act of 2010 that create SLS pretty much said the following (read)
They talk about deep space but they never define a specific mission.
24: Do you think Starliner still has any chance of actually flying astronauts to the ISS with the deorbit date quickly approaching
I'm not sure anybody should be asking me my opinion on Starliner. A year ago I would have said that it made no sense for Boeing to throw more money at it but it looks like they might be, and a non-SpaceX capsule might now be more attractive and important to NASA.
Maybe I'll do a "postest mortem" in the future.
25: What causes the different colors of plumes in rocket engines?
Here are 3 kerolox engines burning RP-1 kerosene and liquid oxygen.
The RD-180 has a yellowish-white exhaust, SpaceX's Merlin has the same, but Launcher's new E-2 engine looks like a methane oxygen engine. What's going on?
26: 40 - Have we already developed the best chemical rocket engines, or are there future development pathways for chemical rocket engines?
27: 5 - Are satellite constellations like Starlink actually sustainable or just a gold rush bubble?
28: 6 - Why is Mars a bad place for human habitation?
29: 3 - What do you think of mars cyclers? A large space station that flys a delicate free-return orbit swinging back and forth between Earth and Mars. The idea is a crewed ship would rendezvous with the station which would travel to the other planet and provide all the necessary life support and equipment for deep space coasting, allowing reuse of deep space infrastructure and lower the cost of individual missions.
30: 1 - What do you know about micro-gravity manufacturing?
31: 1 - What are some of the technical complexities of orbital refueling? And has anyone achieved it in the past, before starship and blue origin
32: 0 - Any thoughts on Chemical Cislunar Tugs, refueled from NEOs and/or processed Lunar Regolith
33: 5 - Outside of internet/observation what commercial markets are promising in the satellite industry
34: 0 - Would Falcon Heavy be a cost effective alternative to Starship for a thousand 50 ton payloads to LEO?
35: 0 - In the future if nuclear fusion ever becomes practical and modular would it open up new possibilities for engines?
36: 0 - Could Auriga Space succeed?
37: 0 - Why is Starship V2 such a disaster?
38: 0 - Do you think Starship will ever carry humans? I'm concerned about its vulnerability to debris impacts and its complete lack of redundancy.
39: 0 - Would launching 2 starships to mars as A part of A single 2 stage craft allow for more mass to be delivered Then 2 separate launches? Would it be practical?
40: 0 - make an analysis of having orion drive interceptors tipped with tungsten and a camera science payload standing by in orbit to catch up with interstellar vistors like i3 altlas or to smash incoming rocks/formics
41: 1 - Can you do a video on rotovators and maybe the ones tethers unlimited might do. I dream of 100s of short 20km rotovators flinging starships in stacked shelled orbits to go beyond the tyranny of the rocket equation. It also means you must bring back mined mass to fling out more ships.
42: 0 - Do you think rotating detonation engines would be feasible (in terms of manufacturing, economy, and performance) for a mass produced rocket, like Falcon 9?
43: 1 - What are your thoughts on the possibility of spacex hosting customer payloads on starlink satellites? How might this effect the launch market?
44: 1 - How could things change for SpaceX and space in general if next term a democrat becomes president?
45: 0 - How will starship come back from mars? Would it need to refuel in low mars orbit? How much radiators will it need to stop cryogenic fuels form boiling off?
46: 0 - Which approach for full reusability is more feasible, realistic, easy to realise - Starship or StokeSpace's Nova?
Maybe there some other ideas for full and rapid reusable vehicles?
47: 0 - For the near term and probably the medium term, all we will want to get back from the lunar surface is information, samples, and astronauts. Starship and even Falcon 9 seem like overkill for this job. Does an expendable ascent vehicle make economic or logistic sense?
48: 0 - In your opinion, as of pre launch of Starship Ift 10, has Spacex learned enough from the past few launches(attempts) to have a better or worse track record with block 3 starship compared to block 2 starship?
49: 1 - How do you think we could make human spaceflight actually cheaper and have a good business case? I know that many people will default to "robots better" but I've always felt that to be an oversimplification that assumes human spaceflight will always remain as expensive and limited as it is now.
50: 2 - How expensive do you expect to be one Starship launch when the system is fully reusable and a few years in service. Some math to support that please? Fuel, people, materials...
51: 0 - Do you plan anything about airbreathing ion engines?
52: 1 - If you could take a vacation on any celestial body in the solar system where are you going?
53: 0 - what kind of infrastructure would be needed to maintain a permanent extraplanetary colony? from short/mid and long term.
54: 1 - Could heat pumps be used to increase the temperature of waste heat to make radiators more efficient
55: Why weren't Methalox engines as popular in the past as they are today?
