The thread for space cadets!

[hobbsyoyo]

It won't be able to compete in most situations, unless we broaden the definition of 'compete' to include government mandates. That's already going on - the Europa Clipper mission has been mandated by Congress to launch on the SLS. This was meant to secure uses for the SLS and ultimately provide jobs in Louisiana and Alabama. NASA is actually trying to push back on this requirement by pointing out that the version of SLS that would be used to carry Europa Clipper likely won't be ready in time and will cost many multiples of what they would pay to launch it on even an overpriced Atlas V. But for now, the law says it has to go on SLS so that's what they are working toward.

The only real situations where SLS could compete with BFR are for missions where the government mandate it or for missions that require payloads so large they won't fit in BFS's proposed cargo bay (and I guess that would be fourth version of BFR/BFS - Mars ship, Tanker, Point-to-Point transport, Payload deployer). So something like Skylab II or various proposals for monolithic space stations (i.e. they don't require assembly) would likely have to go up on SLS since you can't stack a payload on top of BFR/BFS and they would likely be too big to fit inside BFS.

But right now, even without BFR flying, the SLS basically cannot compete with Falcon Heavy (which is real and flying) or New Glenn (which is coming soon). Both rockets are close to the payload range of the SLS and let's not forget that the current version of SLS they are building can't launch payloads; it can only launch the Orion capsule. To get a payload capable SLS, it will be another decade and a few tens of billions more in development cost.

That version of the SLS will be capable of heavier payloads than both FH and NG by a decent margin but it's going to cost a ton of money. And in the end, there are no payloads that actually require that sort of lifting capability. The only thing SLS could really offer that those two can't are direct injection trajectories (i.e. they don't need a bunch of planetary flybys over several years) or for physically very large (but not that heavy) payloads like a giant space telescope that doesn't fold up. And by the time that version is flying the NG 3-stage variant will be flying with a comparable payload to the upgraded SLS (and higher payload than block 1 SLS) and a giant fairing for physically large payloads and likely the BFR/BFS will be flying as well which has a monstrously huge payload (even compared to Block 2 SLS) and a large payload bay in that fourth variant I mentioned.

tl;dr -
It can't compete.


FYI

BFR = Big Falcon Rocket (1st stage)
BFS = Big Falcon Spaceship (2nd stage, where the payload or colonists go)

 

[warpus]

Your post answered my question in so much detail I had nothing at all to add or follow it up with

But I do have this video. Imagine if more people were this excited about rockets, spaceflight, and the future of our species

 

[hobbsyoyo]

The Stratolaunch vehicle completed tax tests on the runway the other day.


This plane has had a very long and difficult development. The original idea was to strap together two 747's, then that was dropped in favor of a custom design. Originally, it was supposed to launch a version of Falcon called 'Falcon Air' but that too was dropped. Then it was supposed to carry a custom rocket from Orbital ATK but that too was dropped. Eventually, they settled on carrying Pegasus XL rockets, which are really very small compared to the airplane. Stratolaunch claims that their plane will enable customers like the air force to launch a complete constellation of multiple small payloads on multiple Pegasus XL rockets at once but I doubt that plan will ever come to fruition. Stratolaunch does have an agreement with NASA to test fire engines at NASA facilities, so it seems like Stratolaunch is developing their own custom rocket.

I guess Paul Allen has big enough pockets to burn through even more cash developing a rocket on top of this gigantic plane.

 

[warpus]

That just looks like something some half-drunk guy would build in KSP

 

[hobbsyoyo]

The James Webb Space Telescope is going to bust through its cost cap (imposed after 2 decades of schedule and cost overruns) and will miss its launch date. The sun shade ripped when they tried deploying it and the thrusters are not working correctly. Good times. Way to go NASA and Northrup. Cost plus for the win.

 

[Thorgalaeg]

The Stratolaunch vehicle completed tax tests on the runway the other day.


This plane has had a very long and difficult development. The original idea was to strap together two 747's, then that was dropped in favor of a custom design. Originally, it was supposed to launch a version of Falcon called 'Falcon Air' but that too was dropped. Then it was supposed to carry a custom rocket from Orbital ATK but that too was dropped. Eventually, they settled on carrying Pegasus XL rockets, which are really very small compared to the airplane. Stratolaunch claims that their plane will enable customers like the air force to launch a complete constellation of multiple small payloads on multiple Pegasus XL rockets at once but I doubt that plan will ever come to fruition. Stratolaunch does have an agreement with NASA to test fire engines at NASA facilities, so it seems like Stratolaunch is developing their own custom rocket.

I guess Paul Allen has big enough pockets to burn through even more cash developing a rocket on top of this gigantic plane.

Cant see the big advantages of launching from an airplane when a conventional rocket reaches 10,000 meters high in seconds. How much propellant are you saving? And then there are all the limitations in rocket size and having to operate giant aircraft. (And design and build them, and if ksp teaches us something is that designing planes is much more difficult than designing rockets)

 

[hobbsyoyo]

Cant see the big advantages of launching from an airplane when a conventional rocket reaches 10,000 meters high in seconds. How much propellant are you saving? And then there are all the limitations in rocket size and having to operate giant aircraft. (And design and build them, and if ksp teaches us something is that designing planes is much more difficult than designing rockets)

Actually, a lot of fuel is burned in the initial climb out. Maybe even a majority of the fuel depending on the particular rocket. Rocket engines are least efficient on the ground, so there's that. Then you're also moving very slowly, which imposes another efficiency penalty due to gravity losses. You're fighting against the thick air, which imposes a drag penalty. Your stack is also fully fueled, so your engines are going at full throttle (a lot of rockets throttle back as they climb to avoid over-acceleration) which burns more fuel.

So there are some big advantages for fuel savings from launching from an airplane. The other big advantage (maybe even bigger than just getting above a lot of the atmosphere) is the fact that the plane can take the rocket to the best spot for launching. It can go to the equator for equatorial launches or out into the ocean where there are no hazards for other launches. That's a huge advantage because there are massive (~30%) fuel savings for equatorial launches and being able to avoid hazard zones simplifies the heck out of launch operations which ultimately saves money.

But then there are obvious drawbacks. The drop from the carrier plane is technically challenging. Then there is a limit on how big of a rocket you can carry. Then you have to figure out how to fuel the rocket if it uses propellants that are cryogenic. And a bunch of other challenges that negate the advantages.

I would be surprised if this plane ever launches a rocket much bigger than a Pegasus XL rocket and really its massively overbuilt for that job.

I'm going back and forth with myself on whether or not airplanes or rockets are harder to design in real life. Everything in aerospace is about saving mass, which is really the route cause of most of the design challenges for both planes and rockets. Over-simplification: In civil engineering, if you find a design deficiency, you throw concrete and rebar at the problem until it goes away. You can't do that with rockets and planes - to the point that aerospace uses a different formulation for 'factor of safety' calculations than other engineering disciplines. And rockets take this to an extreme, which of course makes them harder to design. But most airplanes have pilots and passengers and have to operate over populated areas which are all things rockets don't usually have to deal with, so there is a lot of design challenges posed by that. I think it's a toss-up really.

 

[Cutlass]

How about launches from high altitude mountain regions?

 

[Michkov]

How about launches from high altitude mountain regions?

Getting the rockets up there is a challenge, also the humans living in the crashzones for first and second stage will be an issue. These are two reasons why most launch sites are on the shore, lots of water to safely drop stage into. Sometimes even explode them should something go wrong.
For the US at least I think the infrastructure is setup to deliver the stage along waterways, which also speaks for a shore based launch facility.

 

[hobbsyoyo]

@Michkov is spot on.

 

[Samez]

The Stratolaunch vehicle completed tax tests on the runway the other day.

Spoiler :

This plane has had a very long and difficult development. The original idea was to strap together two 747's, then that was dropped in favor of a custom design. Originally, it was supposed to launch a version of Falcon called 'Falcon Air' but that too was dropped. Then it was supposed to carry a custom rocket from Orbital ATK but that too was dropped. Eventually, they settled on carrying Pegasus XL rockets, which are really very small compared to the airplane. Stratolaunch claims that their plane will enable customers like the air force to launch a complete constellation of multiple small payloads on multiple Pegasus XL rockets at once but I doubt that plan will ever come to fruition. Stratolaunch does have an agreement with NASA to test fire engines at NASA facilities, so it seems like Stratolaunch is developing their own custom rocket.

I guess Paul Allen has big enough pockets to burn through even more cash developing a rocket on top of this gigantic plane.

It reminds me of the Heinkel He111 Z (Zwilling) project of the Nazis.

Spoiler He 111Z :

I could imagine going for a new Antonov Mriya might have been the cheeper version...

Spoiler Antonon An225 :

edit:
I just read that the Chineese were simply faster and bought the parts and rights for further planes

 

[Takhisis]

Can Earth-like planets (same size-mass+solid) have planetary rings?

I just read that the Chineese were simply faster

The trait is called ‘Industrious’.

 

[hobbsyoyo]

Can Earth-like planets (same size-mass+solid) have planetary rings?

The trait is called ‘Industrious’.

Yes. It would be less dazzling since shiny ice wouldn't last long in orbit this close to the sun, leaving it far more dull than Saturn's rings. This could be offset by a moon ejecting geysers to replenish it as happens at Saturn. However, if the world had a moon, that would tend to destabilize the entire ring - replinishment likely would not keep up with natural destruction of the ring in a system around a world as small as the Earth.

It would also make the climate cooler in seasons when it obscures the sun locally.

 

[warpus]

This is neat

(It's an animated rocket exhaust type thing if you're the sort of person who doesn't click anonymous links)

 

[hobbsyoyo]

From the KSP Thread:

I'm trying to build my version of the BFR. I've built the BFR spaceship and am now working on the BFR 1st stage. Took me a while to figure out how to add a docking port to the rocket exhaust part of the spaceship.. but I finally got it

One thing I'm a bit confused about.. Why would the BFR rocket ever need to refuel in Earth orbit? Isn't it possible to get the whole thing in orbit using the 1st stage, without using any fuel at all in the spaceship stage? If not, how will the BFR tanker get in orbit with full tanks of fuel? If it's possible to get the tanker in orbit all in one go, why can't you get the BFR spaceship all in one go? Shouldn't the tanker weigh more than a fully loaded BFR spaceship even?

No, it's too heavy to launch it into orbit fully fueled without burning any of its own propellant. What you're talking about is an SSTO launcher and while those are possible (the Falcon 9 S1 could actually do this), the payload they could bring to orbit with them is basically nothing. SSTO is hard, harder even in real life than in Kerbal and so rockets always have a second stage. For BFR/BFS, the BFS is the second stage and it does have to burn a lot of its own propellant to get into orbit - particularly for a higher orbit that will be stable for months while they stage the whole transit. (Elon has talked about sending a fleet of ships to Mars at once in the style of Battlestar Galactica rather than send one ship at a time).

I assume the tanker will weigh much more than the standard spaceship because the spaceship will have a ton of empty space. But I can't say that for certain because I don't know how much all the life support equipment and other human-centric gear will weigh (it will surely be more dense than Methalox). But anyways, because the tanker will use all of the habitable volume for fuel, it will have a lot of excess fuel once in orbit. The habitation section of the spaceship is easily 1/3 or more of the volume of the overall ship - so that's a lot of room for extra fuel. I do believe that each ship will require more than one tanker to fully top off, however.

 

[warpus]

Interesting. So the BFR tanker getting into orbit will use up even more fuel than the BFR spaceship (since they use the exact same 1st stage), but since the BFR tanker has a lot more room for fuel, it will end up in orbit with enough fuel to refuel any BFR spaceship.

That's all way too carefully designed. I might have problems doing this by eye

 

[hobbsyoyo]

Interesting. So the BFR tanker getting into orbit will use up even more fuel than the BFR spaceship (since they use the exact same 1st stage), but since the BFR tanker has a lot more room for fuel, it will end up in orbit with enough fuel to refuel any BFR spaceship.

That's all way too carefully designed. I might have problems doing this by eye

The tanker will also be able to use more energy-efficient trajectories to get to orbit since it is unmanned. Manned launches have to fly very careful trajectories to ovoid over-acceleration that can hurt squishy humans and to allow for several abort scenarios that would be impossible under certain flight plans. So it may be the case that the tanker actually burns less fuel to get to orbit. But in any case I'm fairly certain they will use multiple tanker flights to refuel each spaceship so that should make your job easier.

Boeing's Starliner spacecraft required the Atlas V's second stage be redesigned to take dual engines to avoid steep trajectories that would put a lot of stress on the capsule should it have to separate early and land. The new trajectory is less energy efficient but necessary for astronaut safety.

 

[warpus]

Multiple tanker flights to refuel! I don't have time for that! I'm going to try to put together a BFR that doesn't need to have the BFR spaceship part refuelled at all. But I might fail

Interesting about the possibility of getting the tanker into orbit in a more efficient way. I never thought of that

 

[hobbsyoyo]

It turns out that during the Apollo program, scientists kept several sample bags sealed and unopened so that they could be examined by more sophisticated equipment in the future. There is now a debate about whether now is the time to open and examine them. I think it is for a couple of reasons. For one, we do have much more sophisticated equipment now. For another, so long as we're pretending we're going to go back to the moon, we might as well examine the samples to see if they contain anything that would make the areas they came from interesting targets for future landings.

https://www.space.com/39870-should-we-open-sealed-apollo-moon-samples.html

 

[hobbsyoyo]

Multiple tanker flights to refuel! I don't have time for that! I'm going to try to put together a BFR that doesn't need to have the BFR spaceship part refuelled at all. But I might fail

Interesting about the possibility of getting the tanker into orbit in a more efficient way. I never thought of that

Yes, generally for manned missions, you want to keep acceleration as low as possible. You also want to avoid very very steep trajectories because of the added stress they put on the capsules should they have to bail out before getting to orbit. Also, some launch escape systems just aren't effective in some parts of some trajectories due to wind loads, vehicle accelerations and other factors so you try and avoid that if possible. "Puller" type launch escape systems (where the escape system is mounted above the capsule like for Apollo and Soyuz) are particularly susceptible to this. 'Pusher" type systems (where the engines are integrated into the capsule and push from below) are much less susceptible to abort-no-go zones and are used by the Starliner, Dragon 2 and New Glenn capsules. The SLS will use the old puller-type system, as do the Soyuz and Chinese capsules. I have no idea what the Indians will use for their manned launch system under development.

The shuttle had an especially atrocious set of abort scenarios. Once the solid rocket motors were lit, there was nothing they could do until they were jetisoned*. At that point they had a few options and all of them were terrible. There was one abort scenario called 'abort to orbit' that was used once when one of the three engines in the shuttle shut-down early. That shuttle just barely made it to orbit and only did so because an engineer on the ground was able to diagnose a problem in a second engine that was threatening to shut down and overrode the shut down sequence in time for them to still be able to limp to orbit. Had he not been as quick on his feet, the astronauts would have been forced to attempt a landing in Africa which would have almost certainly killed them.

*Actually, the first flight had two ejection seats taken from the SR-71 blackbird that may have saved the Challenger astronauts had they been present for that flight. They were removed for later flights to save mass and complexity. It's also unlikely that they really could have saved the astronauts in many failure modes, they were more of a security blanket than a real solution. I call the shuttle a known death trap for a reason.