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The XLR-99’s that pushed the X-15’s used LOX-NH3 propellants. I do not know the expansion ratio of those engines. What works depends upon the ratio of chamber pressure to ambient pressure at the lowest altitude the engine is designed for.
My ancient Pratt and Whitney Aeronautical Vest Pocket Handbook from Dec 1969 lists data for this propellant combination, among many others. It seems to be as accurate a reference today as it was back then. Isp depends marketedly upon the nozzle expansion conditions, c* depends only upon chamber pressure, and so is a less confusing measure for comparison; although, you have to do your own ballistics (at least in rudimentary form) to get Isp from it via Isp = CF c* /gc. It is CF that is dependent upon the expansion pressure, geometric area ratio, and exit divergence angle (which correction applies only to the momentum terms, not the pressure-area terms).
Quoting from my reference at two chamber pressures with different expansion conditions:
Pc, psia r Tc, R c*, fps Isp, s how expanded
1000 1.41 5580 5880 295 note 1
100 1.41 5260 5790 347 note 2
Note 1: perfect expansion to sea level 14.7 psia, shifting equilibrium
Note 2: perfect expansion into vacuum at Ae/At = 40, shifting equilibrium
“perfect expansion” means using a nozzle kinetic energy efficiency = 1, when it is usually near 0.983
These values more-or-less bracket the practical achievable values; although Ae/At > 40 is possibleMyself, I would use a power-function curve-fit for c* = (5880 ft/sec) (Pc, psia / 1000)^0.006699 from these data. And I would do my own CF calculation more-or-less the way the textbooks have it for my own expansion conditions and calculations, but being very careful to apply my nozzle efficiency only to the momentum terms. Not all the textbooks do this efficiency thing quite correctly, so beware.
I would use a gas specific heat ratio near 1.2 for this, in the absence of any better data. I would use efficiency = 0.5*(1 + cosine(half-angle)) for my nozzle kinetic energy efficiency. Half angle is the conical half angle if a conical nozzle, and is the average of the near-throat and exit half-angles if a curved expansion bell. That ought to get you within a tiny fraction of a percent the right value to use.
That’s just standard real-world ballistics stuff. I used to do this crap (and much more besides) for a living. Solids, liquids, hybrids, ramjet nozzles-only, etc, all the same, no difference. It starts with c* at your chamber pressure.
GW
Thanks GW,
347 s is quite good. Do you think that LOX-NH3 rockets may be a good choice for the RCS of an Orion-drive spaceship, which needs ammonia anyway for the pulse-unit cannon and for the shock-absorbers?
Would that work with NTO in place of LOX, thereby getting rid of the need for cryogenic tankage?
It could be interesting, but I didn't find any data on NTO-NH3 rockets.
Anyway, my interest in ammonia rocket is due to the spaceship I would like to convince for my next hard-sf novel: she has an Orion-drive NNP, so she needs to store a lot of ammonia for running the shock absorbers and the cannon for the pulse units. Using ammonia even as a propellant for the RCS would simplify the plumbings. LOX is also necessary as a reservoir of breathing gas for passengers and crew. So that's why I thought about LOX-NH2 rockets.
http://www.astronautix.com/l/loxammonia.html
Vacuum Isp = 343s. About the same as LOX/kerosene. Density is about 80% of gasoline. Ammonia is toxic, which complicates things. On the plus side, ammonia is a much better coolant than a hydrocarbon, making it easier to design high pressure engines. Nitrogen is not a greenhouse gas, although water vapour is. On balance, ammonia would however appear to be more climate friendly than kerosene. On the other hand, it is highly toxic to marine life.
That was the XLR-99 of the X-15 spaceplane, which was projected for working in high atmosphere and don't have a high expansion ratio. I guess that it would have a quite better Isp with a bigger nozzle.
Hi to all.
In this patent
https://www.google.com/patents/US20140182265
It is written that a LOX-ammonia rocket with an expansion ratio of 100 can reach a specific impulse of 420 s, near to the 460 seconds of LOX-LH2 rockets but without the trouble of LH2 storage. Why this propellant combination was used so rarely?
The trouble with Utopia Planitia is that it's a bit northern and during the winter the climate might be too cold for the astronauts. The goal would be to find a buried glacier near the equator, in places like Vallis Marinaris or Elysium Planitia.
At the moment, a human mission on Titan is far beyond our technology. We have no artifact or device able to work at the low temperature of Titan atmosphere. We cannot build an habitat where the astronauts can stay for one of two days without freezing. We cannot built spacesuits able to insulate their bodies from the cryogenic atmosphere, we cannot built boots able to walk on cryogenic water rocks. To not mention the space voyage: we surely cannot send humans on Saturn system with chemical rockets: we need something else we still don't have, like gas-core NTR or Orion NPP.
Vive versa, on Mars equator the climate is quite fair and we might be able to send human there at 2030 if we start now investing money for projecting and building space vehicles, landers and habitats.
Considering that the habitable zone of a tidally locked planet is near the terminator, would it be better to chart them using a modified Mercator projection, putting the cylinder tangential at the terminator instead at the equator?
In this way we will have 90 stellar parallels in the day-side and 90 parallels in the night side, with the inhospitable sub-stellar and anti-stellar poles expanse, but the habitable zone near the terminator well represented.
I'm not an expert and I'm very interested in knowing your opinion.
Thanks to all
Quaoar
Here is explained why quantum entanglement cannot be used to send FTL messages
Not completely useless, though undoubtedly less useful. Right now, the round trip communication time between Earth and Mars makes rovers slow and cumbersome. The amount of distance they can cover and therefore the amount of science you can get out of them is inversely proportional to round trip comms time.
But why not land on Phobos or Deimos? An orbit to orbit vehicle is undoubtedly easier and a Phobos base would be a beach head that would assist manned exploration of the planet later on.
If they want to stay for more than two year in Mars orbit they need a bigger habitat with artificial gravity, otherwise the crew will suffer very serious health and mental damage. With a view to accept such an outcome, it may be less and less expensive to openly send an expendable crew in a one way mission.
Don't know much about quantum stuff. I just know that it's usually multiple decades between a physics lab experiment and any sort of practical device.
GW
They don't land. They have no artificial gravity. They spend more than two yeras at zero gee in an orion capsule. I think they will become insane before they will be crippled during the 14 gee reenter.
This mission is completely unuseful. For less and less the money it needs they can send an unmanned rover of 10 tons, equipped with a lab for saercing trace of life.
So it would be safer to use gloves. However, fission fragments are so radioactive that you want several feet of water between you and it. That makes cleanup far more problematic. So the "launch cold" thing was not to prevent radioactive exhaust, it was planning for catastrophic failure.
I think catastrophic failure is an issue not impossible to deal with: Apollo 13 Lunar Module RTG generator is somewhere in the indian ocean, but it's still integer and no plutonium has leaked utlil now despite its unexpected atmospheric entry, because it was projected to not crash in case of launch failure. In the same way, it may be possible to project the NTR SSTO core to survive (or be ejected and parachuted) in case of launch failure.
You could use a space fountain, the real problem is the escape velocity, not the gravity, although the gravity would be uncomfortable for humans. Just imagine you have a stream or particles in orbit around this planet, then you encapsulated them in a tube that stretches forming a perfect seal that keeps the atmosphere out. Now you shrink the diameter of that tube, while slowing it down so that it is stationary relative to the surface of the planet. The particles accelerate to faster than orbital velocity but are held to their orbital path by the circular tube, the centrifugal force supports the weight of the tub against gravity. The tube lowers until it is well within the troposphere of the planet, completely encircling it, and an air breathing vehicle takes off from it and lands on the planet's surface. When the mission is complete, it takes off and lands on the tube, the tube then stretches and rises into space, the tube accelerates by slowing down the particles inside until both are once again in orbit around the planet, then a high efficiency plasma drive takes a shuttle back to the mothership. The space fountain is rolled up after disassembly in orbit, and it is on to the next planet!
Another option may be an NTR SSTO with a mass ratio of 5 or 6 capable of an initial acceleration of 2.5 gee: a LOX afterburner may be used in at take-off. I've read a study about a foam-core NTR, using an uranium tricarbide foam with almost the same T/W ratio of the old Timberwind but without the hot spot problems, but I cannot find the reference.
A compact drug assembly factory
Why would you not use an NTR for launch? Obviously you'd need to solve the thrust issue, but the Isp is there to do it in a single stage.
Yes a solid core NTR with an exaust velocity of 10 km/s can reach almost 16 km/s of delta-V with a mass ratio of 5, but with a surface gravity of 2 gee there are a lot of gravity losses and I guess a NTR-SSTO also needs some kind of chemical side busters even with a LOX afterburner.
Alternatively, you could use beamed power from an orbiting station, to create a virtual space elevator, going with Josh's suggestion to head to stationary orbit to keep it in line of sight.
This is probably the best option for a civilized planet with a well extabilished human colony, but I guess it is difficoult to built all the facilities needed in the first exploration mission.
Excuse me, I realize that this topic is a bit hypothetical, but as an ameterur SF writer I'm very courius about it. If some day we will have some sort of FTL drive and we will reach some superearth like Gliese 832c ( https://en.wikipedia.org/wiki/Gliese_832 ) what kind of lander can we use?
Gliese 832c has a mass of 5.7 Earth mass. Its radius is not known but I assume as worst case something like 1.5 Earth radii and a surface gravity of 2 gee. Surface to orbit delta-V is almost 14.6 km/s that easly become 18-20 with air and gravity drag.
I also hypothize its atmosphere is very dense, with a surface pressure of 3 bar, 16% oxygen, 83% nitrogen and 0.93% argon (these data are completely arbitrary but I choose them to allow my characters to survive).
FTL drive is some sort of magic box that move the starship from a star system to another, but it doesn't function in gravity well, where starships has to use convetional nuclear fission rocker, solid core, vapor core or gas core because they still don't have fusion (or they have but is too massive to be used on a starship).
There is alien life on the planet, so using gas-core rockets in and near ist atmosphere is illegal, so I hypotize that a lander has to use a simple rotor with tip-jets for descend and three expendable stage for coming back to orbit: 1st chemical LOX-LH2 rocket, 2nd vapor core NTR with LOX afterburner, 3th vapor core NTR. 2nd stage vapor core is transferred to first stage before jettison, to not contaminate planet atmpsphere. The lander should land almost empty and use local water for ISRU, using some RTG and/or solar panel.
I'm very interested in your opinions,
Thank to all
If it was "safe enough" for a 7-crew shuttle, why not for more on board? I guess it really boils down to how much risk one wants to take to achieve some end result. There's still nothing about rocket flight that is really "safe" in the sense most civilians use that word.
I would think that there is at least as much reason for concern about the turbopump assemblies on the liquid rocket engines of almost any configuration we care to think about. Those are inherently short-life items. And if vigilance relaxes (or even if luck just goes bad), it can fail on the one flight. The refurbished Russian engines did exactly that to Orbital Science's booster rocket a few months ago. Fortunately, no one was aboard.
GW
Even in expander cycle?
Orbitec corporation has built an interesting rocket where oxydizer is tangentially injected in the chamber, forming a vortex insulating the wall. Fuel is injected centrally in the middle of the vortex, keeping the combustion far from the chamber wall.
http://www.gizmag.com/orbitec-vortex-li … ine/24807/
Orbitec is also developing a stoichiometric LOX-LH2 engine (F/O ratio =8) using vortex injection to protect the chamber form higher combustion temperature
http://www.orbitec.com/documents/SCORE_2006.pdf
A stoichiometric LOX-LH2 rocket may be very interesting for the possibility to use water propellant depot to be hydrolyzed before use.
Orbitec is also developing an interesting microwave electric thruster using water as propellant that can be used with the stoichiometric rocket: using the rocket to leave Earth orbit and the electric thruster to shorten the trip
I dunno myself. Sounds like a Zubrin thing, though. Could be quite good, maybe not.
The first thing I though about was trace unreacted nitrous oxide getting into the oxygen. Another name is "laughing gas". It doesn't take much to make a person completely incompetent. That was the first anesthetic used in dentistry.
GW
Zubrin claims this composition for the breathing gas:
COMPONENT CONCENTRATION (MOLE %)
N2 66.83%
O2 31.56%
N2O 0.11%
NO2 1.0 ppm
NO Not detected
0.11% of N2O is not enough for anaesthetic effects, but it can inactivate B12 vitamin by oxyding its cobalt atom, so astronauts may have to take an extra B12 vitamin supply. Anyway N2O may have other side effects in chronical exposition, if astronauts only breath air from N2O during a long mission. And I'm also concerned about trace of very toxic ruthenium oxide cathalist in breathing mixture.
But it can be a very good monopropellant for a MMU, with the possibility to use the propellant as an emergency oxygen supply.
An interesting device from Robert Zubrin, who proposes to store oxygen as liquid N2O (21°C and 50 bar) instead of gOX.
Zubrin's back-pack has liquid N2O tank (8 kg is enough for eight hours) lighter than a compressed gas rank, a reactor with a catalyst bed and a little compressed air reservoir.
Dr. Zubrin proposes to use N2O to produce breathable 33%O2 66%N2 air, or to produce 100% O2 for breathing and use the N2 for cooling and for manuevering cold gas thrusters.
https://www.google.com/patents/US7165546
I dunno, Louis. The jury may still be out on that one. Airbus is far behind (and likely not yet well-funded to do this), but Spacex has already run into repeated difficulties solving their far more demanding recovery problem. We'll have to see how this plays out over time. On a scale of years.
My opinion is that Spacex has made their problem more difficult than it needs to be by two possible flaws in their approach. (1) Not having a low-enough 1-engine thrust to permit hover, means that they cannot slow down touchdown timelines to recover from unplanned off-design attitude, speed, and location excursions. (2) I rather doubt that engine gimbal has the authority and the speed to control attitude upsets right at touchdown (I bet they will eventually need attitude thrusters for that). Those grid fins are useless for slow-speed attitude control.
Their problems about landing that stage have less to do with their admittedly very fine expertise in rocket engines, and a whole lot more to do with the control of flight vehicles at less-than-optimal conditions. That's the same area that caused them stage separation troubles with Falcon 1, when they first got started several years ago.
GW
Hi GW
It's ever a pleasure to read your posts.
It seems to me SpaceX is at a dead point, being unable to recover the first stage without redesign it, adding low-thrust rockets for hovering and more powerful attitude control rockets to counteract strong winds. But all these upgrades have a R& D cost and add more weight reducing the payload.
It takes an experienced old hand on your staff to sort out troubles like that. Spacex does not like to hire anyone but "young turks" under 40-45 years of age, because they like to work them 60 hours a week, and older guys won't or can't be worked that way. It's a management staffing approach that serves them well much of the time, but occasionally shoots them right in the foot.
GW
Why not to simply hire experienced old guys as consultants to solve specific problems?
I have found this interestin video about Airbus Adeline semi-resuable system
http://www.dailymail.co.uk/sciencetech/ … eline.html
The main LOX-LH2 engine and the avionics of a new version of Ariane are pleaced inside a winged nacelle, that detaches from the first stage tank, reenters and lands like a conventional aeroplane using two propellers, resulting up to 30% launch cost reduction.
It may be simpler to make it work than Falcon R resuable first stage.
If it has been observed, it is within the observable horizon.
It has been oberved at it was 12 billion years ago.
This black hole formed when the Universe was only One billion years old.
http://www.cnn.com/2015/02/26/intl_worl … lack-hole/
It is the most massive black hole ever found, the question is, is it still around today? Could we go there in a spaceship? Lets suppose we could accelerate at 1-g indefinitely, probably this black hole was about 12 billion light years away, it is receding from us as the Universe expands, Probably by the time the starship has traveler 12 billion light years, the Universe would be 25 billion years old. Probably the black hole would be further away by the time we traveled that distance, they say the Universe's expansion is accelerating, but is it accelerating at 9.8 meters per second squared away from us at that distance? I suspect the black hole would still be there by the time we got there, but it would no longer be a quasar. I think some version of an interstellar ramjet would be required. Theoretically with Einstein's relativity that black hole could be reached within a human lifetime.
Probably now it will be beyond obserbable horizon so it will be out of reach without some kind of FTL drive.
There's at least two wildly-different versions of gas core, too.
GW
Which are?
Oil platforms require a bottom to rest upon and be anchored too. If you go far enough offshore, past the edge of the continental shelf, the bottom is unreachable at over 2 miles down. In deep water, a self-positioning barge is the only answer.
To return the stage all the way to launch site requires a lot more propellants. They're already burning off a load just to ease the atmospheric entry speed (that's the 3-engine apogee deceleration burn) and control the fall (that's the long 1-engine burn) with supersonic retro propulsion now.
Stage recovery propellant cuts into payload, but not as much as my first intuition would have suggested. The powered landings they want to do just might be survivable at their low inert mass fractions. Chute landings in the ocean not.
GW
Why not buying some land on a Caribbean island on the rocket course, and land the first stage on it?