For Questions That Don't Merit Their Own Thread

[Nivee~]

How do I calculate forced convective heat transfer coefficient of liquid nitrogen at different velocities??

[magnemoe]

17 hours ago, Brownie352 said:

Are there any current Concepts or in development spacecraft to land people to mars and return them to earth?

Starship is the obvious one. Plenty of concepts but none has build anything, that is outside of on earth test of living on an small mars base. 

[Mad Rocket Scientist]

On 4/28/2019 at 3:36 PM, Brownie352 said:

Are there any current Concepts or in development spacecraft to land people to mars and return them to earth?

Off the top of my head, these are the ones farthest along:

SpaceX is currently building flight prototypes for a ship that could land humans on mars.

They intend to build a mars colony as soon as physically possible, to the point of building rockets in a field in Texas. They currently have the cheapest and most technologically impressive rockets flying. They plan to launch humans to mars by 2024, which is wildly optimistic.

NASA is currently building a launch vehicle that could launch a crewed mars mission, although there's not really a lander yet.

Complex politics and cost and schedule overruns, along with a design that looks a lot like previously cancelled designs makes a lot of people think that their plans will be cancelled before they get to mars. Their target date is 2033, which they might be able to achieve if the program doesn't get cancelled, and gets as much funding as they require (way more than they've had at any point since the Apollo program, and possibly even more).

Blue Origin is developing (and building engines for) a launch vehicle that could also launch a crewed mars mission.

They do not explicitly state a mars landing as part of their goal, rather "millions of people living and working in space." They basically have unlimited funding from Jeff Bezos, and if they're in the position to, will almost certainly try for a mars landing.

The European Space Agency, China, and Russia also all have plans to the right of 2040, approximately.

This is a pretty good rundown the history of all this: https://en.wikipedia.org/wiki/Human_mission_to_Mars

[ARS]

Is it possible to build a rocket engine (small size) using purely oxygen combustion? Aka the engine is powered by oxidation of oxygen which, after initial combustion on air will be self sustaining by continuous oxygen supply

[magnemoe]

1 hour ago, ARS said:

Is it possible to build a rocket engine (small size) using purely oxygen combustion? Aka the engine is powered by oxidation of oxygen which, after initial combustion on air will be self sustaining by continuous oxygen supply

Are you thinking of air augmented rocket?
Yes its possible, some even exist and is used. 
Basically you burn fuel rich and the rest of the fuel burn with the oxygen in the air. This even work for solid fuel. 
Downside is that this don't works so well then then air pressure changes a lot as it does in rocket launches so mostly used in missiles. 

[ARS]

2 hours ago, magnemoe said:

air augmented rocket?

Yes, that one. If it isn't work well for rocket launch due to the performance issue, what's the advantage of using it on missiles compared with normal solid propellant?

[p1t1o]

19 minutes ago, ARS said:

Yes, that one. If it isn't work well for rocket launch due to the performance issue, what's the advantage of using it on missiles compared with normal solid propellant?

Rockets dont spend a lot of time accelerating in-atmosphere, in fact they are supposed to get out of the air as soon as they can, so much of that extra plumbing is dead weight for most of the trajectory. Missiles (with certain exceptions, such as ICBMs or ASATs) travel in a much more horizontal path, spending the entire time within the atmosphere where they are able to take advantage of atmospheric oxygen.

[Terwin]

2 hours ago, ARS said:

Yes, that one. If it isn't work well for rocket launch due to the performance issue, what's the advantage of using it on missiles compared with normal solid propellant?

The advantage is you can carry less weight, as you are using some oxygen which is not being carried(and accelerated) on your rocket.

Due to the rocket equation, less weight is a major benefit, and using atmospheric oxygen(and general atmosphere for reaction mass) is what allows airplanes to have more than ten times the ISP of rockets. ( > 8000 vs 400-500)

(see the chart here: https://en.wikipedia.org/wiki/Specific_impulse )

 

[wumpus]

2 hours ago, p1t1o said:

Rockets dont spend a lot of time accelerating in-atmosphere, in fact they are supposed to get out of the air as soon as they can, so much of that extra plumbing is dead weight for most of the trajectory. Missiles (with certain exceptions, such as ICBMs or ASATs) travel in a much more horizontal path, spending the entire time within the atmosphere where they are able to take advantage of atmospheric oxygen.

As far as I know, the Soviet Gnom program (an ICBM) was the only attempt to make an air augmented rocket and was canceled in 1965 before flight tests.  While the rocket may spend little time in the atmosphere, expect it to consume 1/2 to 3/4 of the fuel while doing so.  Changing the Isp of the rocket from kerolox level Isp to hydrolox level Isp should have some cost advantages, but don't appear to be enough to overcome the issues of designing the aero intakes to handle the wildly varying situations.

33 minutes ago, Terwin said:

The advantage is you can carry less weight, as you are using some oxygen which is not being carried(and accelerated) on your rocket.

Due to the rocket equation, less weight is a major benefit, and using atmospheric oxygen(and general atmosphere for reaction mass) is what allows airplanes to have more than ten times the ISP of rockets. ( > 8000 vs 400-500)

(see the chart here: https://en.wikipedia.org/wiki/Specific_impulse )

Unfortunately the air-augmented rocket's Isp is more like 400-500 (and anything not using RS-25 based engines is well under 400 during atmospheric flight) which means that you don't get the huge benefits of Ramjets and similar (of course it should be significantly easier to design and manufacture).  The idea is simply to heat the atmospheric air and use it as a propulsion medium rather than just the water and carbon dioxide reaction products.

[Nivee~]

Can someone please please help me figure out the thermophysical properties of liquid nitrogen? I looked up google scholar but I can't find anything...

Edit: Oh nevermind, found it~

https://apps.dtic.mil/dtic/tr/fulltext/u2/275728.pdf

The problem: It's in imperial!!!

Edited April 30, 2019 by Nivee~

[Gargamel]

So, the Really Deep Basement thread over in games got me thinking.   Eventually it will reach the core of the planet.   And as you get closer, Gravity should decrease.   Not pressure, but gravity.   One thing led to another, and I had this thought....

So what happens when you reach the barycenter of a system?   How easy would it be to park a satellite at the barycenter of a binary system (a la Pluto/Charon)?   Would this make a good "station" to act as a stop over point on a dual body space elevator if it was hinged properly to account for the slight movement in two tidally locked bodies?   Imagine the awesome sci-fi scenarios that could come from this...

[magnemoe]

1 hour ago, Gargamel said:

So, the Really Deep Basement thread over in games got me thinking.   Eventually it will reach the core of the planet.   And as you get closer, Gravity should decrease.   Not pressure, but gravity.   One thing led to another, and I had this thought....

So what happens when you reach the barycenter of a system?   How easy would it be to park a satellite at the barycenter of a binary system (a la Pluto/Charon)?   Would this make a good "station" to act as a stop over point on a dual body space elevator if it was hinged properly to account for the slight movement in two tidally locked bodies?   Imagine the awesome sci-fi scenarios that could come from this...

It would be an unstable lareng point same as L1, 2 and 5. pretty useful as we use them for multiple satellites. You need some fuel for station keeping same as in GEO

[Snark]

21 hours ago, Gargamel said:

So what happens when you reach the barycenter of a system?   How easy would it be to park a satellite at the barycenter of a binary system (a la Pluto/Charon)?   Would this make a good "station" to act as a stop over point on a dual body space elevator if it was hinged properly to account for the slight movement in two tidally locked bodies?   Imagine the awesome sci-fi scenarios that could come from this...

Nothing special about that point. Note that assuming the two bodies are of unequal masses, the barycenter will be closer to the more massive one, so gravity at that point will be definitely lopsided, pulling it towards the heavier one. Depending on the mass disparity, the separation between the two bodies, and the radius of the more massive one, you may be on a suborbital trajectory and go splat, or you may miss it and end up on some funky orbit (likely flung out of the system entirely).

For example, the barycenter of the Earth-Moon system happens to be inside the Earth, but if the Moon were a bit more massive and/or farther away, the barycenter could be above Earth's surface. Suppose it were at an altitude of, say, 10 km above sea level. If you put an object there, what would it do? Answer: it would just fall down, at about 9.8 m/s2, same as it would if you placed it 10 km above sea level anywhere else on Earth. Yes, there would be a horizontal component to its velocity (assuming you placed it at rest relative to the barycenter), but that would be pretty slow and nowhere near orbital speed.

TL;DR: there's not really anything special about the barycenter in this regard.

[Gargamel]

33 minutes ago, Snark said:

TL;DR: there's not really anything special about the barycenter in this regard.

[BillKerman123]

Does anyone know how to calculate the kinetic jet energy rate per unit flow of propellant in a rocket engine given its thrust, propellant consumption per second, the velocity of the vehicle, and the energy content of the propellent assuming 100% combustion efficiency? Yes, that's a question straight from Rocket Propulsion Elements. 

[Flibble]

2 hours ago, BillKerman123 said:

Does anyone know how to calculate the kinetic jet energy rate per unit flow of propellant in a rocket engine given its thrust, propellant consumption per second, the velocity of the vehicle, and the energy content of the propellent assuming 100% combustion efficiency? Yes, that's a question straight from Rocket Propulsion Elements. 

Yes.

Jet power = ½F²/dm, where F is thrust and dm is mass flow rate.

Divide by mass flow rate for jet energy per unit flow.

[ZooNamedGames]

Probably been asked before, but how did the Energia compensate for offset launch masses? The Space Shuttle (since that's the closest comparison I know of) compensated with a widely ranging gimbal from the RS-25 rocket engines. I'm not aware of the RD-170 (boosters) or the core engines RD-0120 being able to gimbal that significantly. So how did the Energia launch vehicle compensate for such bulky masses such as the Buran and the Polyus? Especially since the Buran was not equipped with engines to provide any thrust during launch.

[DDE]

On 4/30/2019 at 4:25 PM, wumpus said:

As far as I know, the Soviet Gnom program (an ICBM) was the only attempt to make an air augmented rocket and was canceled in 1965 before flight tests.

Meteor and several other upcoming air-to-air missile sport air-augmented solid motors.

20 hours ago, ZooNamedGames said:

Probably been asked before, but how did the Energia compensate for offset launch masses? The Space Shuttle (since that's the closest comparison I know of) compensated with a widely ranging gimbal from the RS-25 rocket engines. I'm not aware of the RD-170 (boosters) or the core engines RD-0120 being able to gimbal that significantly. So how did the Energia launch vehicle compensate for such bulky masses such as the Buran and the Polyus? Especially since the Buran was not equipped with engines to provide any thrust during launch.

RD-170 has +7°...-8° gimbal. RD-0120 had +7°...11°. Cf. Gubanov.

[wumpus]

12 hours ago, DDE said:

Meteor and several other upcoming air-to-air missile sport air-augmented solid motors.

The US Navy fielded the Talos ramjet missile from 1958-1979.  Going to air-augmentation should be seen as a step backward for missiles.

Missiles should be able to fly at fairly specific velocities, although air-to-air pretty much means completely uncontrolled altitudes.  But the Talos was surface-to-air, so presumably could operate anywhere a MiG could.  This is mostly a different problem than maximizing delta-v while getting out of the atmosphere, but hopefully ULA will someday hire someone who worked on one of these.

One thing to remember about any fuel-efficiency ideas: the fuel (and oxidizer) in a falcon 9 is said to be ~$200k.  The fairing is $6M.  Expect Mr. Stevens to spend a great deal more time trying to catch a fairing (whether or not it will be eventually required) than any attempt to apply air-augmented shrouds on a rocket for cost efficiency reasons (although I'd assume that reducing the size of the booster wouldn't hurt overall costs).

[Racescort666]

I wasn’t sure where to put this random thought so here goes in this thread: do you suppose reusable space launch vehicles weren’t developed earlier because most early rocket development was focused on weapons? No reason to recover a booster because you’ll probably not need it again. I know that there were other proposals for hardware to be reused in a manned space program but the first effort resulting in something resembling reusability is Space Shuttle which was designed to be manned from the ground up. I just found this progression of events interesting.

[Terwin]

23 minutes ago, Racescort666 said:

I wasn’t sure where to put this random thought so here goes in this thread: do you suppose reusable space launch vehicles weren’t developed earlier because most early rocket development was focused on weapons? No reason to recover a booster because you’ll probably not need it again. I know that there were other proposals for hardware to be reused in a manned space program but the first effort resulting in something resembling reusability is Space Shuttle which was designed to be manned from the ground up. I just found this progression of events interesting.

It probably has a lot more to do with portable processing power and relative costs.

The ability to handle a vertical landing requires real-time reactions to undesirable changes in altitude latitude and longitude, with high precision when operating at often super-sonic speeds.

On top of that, you need the driving interest to be cost/profit related, which generally means corporate rocket programs.  If no company/private citizen is willing/able to invest in developing their own rocket program, then you will not have a cost-driven program with a vested interest in re-use.

You notice that after the technical advancement and financial success of the .com boom, we got multiple companies working on this problem all at about the same time.

[Nightside]

33 minutes ago, Racescort666 said:

I wasn’t sure where to put this random thought so here goes in this thread: do you suppose reusable space launch vehicles weren’t developed earlier because most early rocket development was focused on weapons? No reason to recover a booster because you’ll probably not need it again. I know that there were other proposals for hardware to be reused in a manned space program but the first effort resulting in something resembling reusability is Space Shuttle which was designed to be manned from the ground up. I just found this progression of events interesting.

Well ICBMs are antithetical to reuse of... anything. Whether they do their job or not, you don’t get a chance to launch again. I’d guess storabilty was a bigger design factor than reusability.

Does any know the ratio of ICBM:non military rockets built?

[Flibble]

2 hours ago, Nightside said:

Well ICBMs are antithetical to reuse of... anything. Whether they do their job or not, you don’t get a chance to launch again. I’d guess storabilty was a bigger design factor than reusability.

Does any know the ratio of ICBM:non military rockets built?

The storability vs efficiency tradeoff for ICBMs and Space launch vehicles meant they diverged almost entirely by the early 60s. The US at least had solid fuelled ICBMs by 1962 at which point they were less interested in making large liquid fuelled rockets. The shuttle program kicked off in the late 60s, not really that large a gap from when missile development diverged.

[Terwin]

2 hours ago, Nightside said:

Well ICBMs are antithetical to reuse of... anything. Whether they do their job or not, you don’t get a chance to launch again. I’d guess storabilty was a bigger design factor than reusability.

Does any know the ratio of ICBM:non military rockets built?

According to: https://en.m.wikipedia.org/wiki/Intercontinental_ballistic_missile#/media/File%3AIcbm-hist-en.png

6287-6297 land-based ICBMs have been deployed as of the end of 2014(with ~ 801-811 deployed at the end of 2014)

According to http://www.planet4589.org/space/lvdb/index.html

70780 launches. The launches include 5741 orbital launch attempts, 28500 suborbital launches, and 36539 endoatmospheric flights.

 

So looks like slightly(~10%) more ICBMs than orbital launches, but far(~4.5x) more suborbital launches than ICBMs.

At this scale, the 14 reused boosters by Space X have much impact on the numbers, but this also counts every deployed ICBM even if it was never launched, but this does not cound rockets that were built but never launched(like those 2 Saturn 5's we still have here on earth) 

[magnemoe]

1 hour ago, Flibble said:

The storability vs efficiency tradeoff for ICBMs and Space launch vehicles meant they diverged almost entirely by the early 60s. The US at least had solid fuelled ICBMs by 1962 at which point they were less interested in making large liquid fuelled rockets. The shuttle program kicked off in the late 60s, not really that large a gap from when missile development diverged.

This is true however at this time rockets had evolved from ICBM, it was still an time for rapid change and time was more important than money so no reason to develop reusablility yet. 

Then it was two traps, the first was SSTO, who is an obvious fail with current technology. Second was that wings was needed for reuse. Yes fold-able wings works for cruise missiles it does not work well for something the size of an passenger plane coming in hypersonic. Then add fat cats who did not see any reason to change. Current rockets worked well enough for com and spy satellites and the random probe.
They tried with the space shuttle but it was run by an committee, with very different objectives and pushed the envelope way to hard, kind of defined hangar queen.