stunthanger.com
General control line discussion => Open Forum => Topic started by: Tim Wescott on November 24, 2015, 10:44:29 AM
-
https://www.youtube.com/watch?v=9pillaOxGCo (https://www.youtube.com/watch?v=9pillaOxGCo)
-
I would prefer to go for a ride in the booster. It is less crowded with all those obnoxious tourists and their video cameras.
Is there a phone nr. where I can sign up?
-
I would prefer to go for a ride in the booster. It is less crowded with all those obnoxious tourists and their video cameras.
Is there a phone nr. where I can sign up?
-
Maybe you could buy a whole ride for you and your family.
I suspect that they figure that getting a booster that's man-rated just for ascent is easier than one that's man-rated for both ascent and descent. Getting tourists to fund space technology is an interesting idea -- I wonder how it'll work out, particularly after the first few really impressive accidents.
-
Maybe you could buy a whole ride for you and your family.
I suspect that they figure that getting a booster that's man-rated just for ascent is easier than one that's man-rated for both ascent and descent. Getting tourists to fund space technology is an interesting idea -- I wonder how it'll work out, particularly after the first few really impressive accidents.
With proper funding this could be a lot closer than you might think!
Randy Cuberly
-
Ah, wasn't that all computer generated animation?
MM
-
It's for real.
https://www.blueorigin.com/news/news/blue-origin-makes-historic-rocket-landing
-
Ah, wasn't that all computer generated animation?
Judging from how it looked, the people in the capsule were but the rest was real. I suspect that they're trying to drum up enough money to get the booster to the point where it can be man-rated.
-
I don't see how the capsule can land soft enough with just a parachute and no braking rockets.
-
It didn't show how it re-enters the atmosphere. It went from outer space to parachute, you skipped a step there.
MM
-
http://www.msn.com/en-us/video/wonder/jeff-bezos-company-blue-origin-just-made-space-flight-history/vi-BBnozT3?ocid=U147DHP
SK
-
At least it's Internal Combustion powered, and not using some electron mumbo-jumbo, Jimbo. S?P Steve
-
It didn't show how it re-enters the atmosphere. It went from outer space to parachute, you skipped a step there.
There's nothing too special there, the "re-entry" heating is not terribly significant. Basically they are dropping in from a dead stop at 62 miles. You could make a back-of-the-envelope calculation assuming no drag until it gets to about 30 miles. I get about 3500 fps which would not generate too much heat load.
The capsule does seem to hit pretty hard. Most of those intended to land on solid ground had either big airbags or terminal braking rockets like the Russians. And they all had contour couches with shock absorbers. Mercury even had an airbag for splashing down in the water.
Brett
-
There's nothing too special there, the "re-entry" heating is not terribly significant. Basically they are dropping in from a dead stop at 62 miles. You could make a back-of-the-envelope calculation assuming no drag until it gets to about 30 miles. I get about 3500 fps which would not generate too much heat load.
The capsule does seem to hit pretty hard. Most of those intended to land on solid ground had either big airbags or terminal braking rockets like the Russians. And they all had contour couches with shock absorbers. Mercury even had an airbag for splashing down in the water.
Brett
I think the intention here was to spend the money on the rocket braking and stabilization system and the necessary controls to make that function. The capsule is likely still "putty".
Randy Cuberly
-
Ah, wasn't that all computer generated animation?
MM
A simple search of the web would have told you it is in fact real.
-
I think the intention here was to spend the money on the rocket braking and stabilization system and the necessary controls to make that function. The capsule is likely still "putty".
Perhaps. The control system for descent is probably the same for the descent as it is for ascent. Note that, just like SpaceX, the control when first activated for landing has very poor transient response and damping. That's almost certainly because the ascent control law is never presented with a large initial error, and the descent will generally always have a large initial error, and they are running into the nonlinearities of limited gimbal travel and limited gimbal rate with large initial errors. You can see the gimbals apparently peg out. That seems to be the/a problem with SpaceX as well.
The inputs for descent are different. You can almost mark the modes as they change - first, acquire and maintain a 0-AoA attitude, then start fiddling the throttle to come to a stop at some fixed low altitude, then, terminal guidance to translate to the landing pad, then acquire a fixed terminal descent rate until touchdown.
As anyone who has played Lander knows, the most fuel-efficient way to land is wait until the absolute last moment, then go to full throttle just high enough to stop before you hit. Just watching, it looks like it's plummeting out of control for a few seconds.
The exhaust changes color because they are adjusting the mixture ratio and flow rate to alter the thrust. The yellow and black smoke is where it goes very rich as the mixture ratio shifts. Throttling these types of engine is a very tricky matter, you can't just adjust the feed pressure up and down to anything you want because they are generally stable only over a narrow range. The Apollo descent engines were the pacing item in the moon landing because they had trouble getting the throttle to work of a a reasonable range of settings. As it was, it was not permissible to run something like the range between 10 and 40%.
Brett
-
Perhaps. The control system for descent is probably the same for the descent as it is for ascent. Note that, just like SpaceX, the control when first activated for landing has very poor transient response and damping. That's almost certainly because the ascent control law is never presented with a large initial error, and the descent will generally always have a large initial error, and they are running into the nonlinearities of limited gimbal travel and limited gimbal rate with large initial errors. You can see the gimbals apparently peg out. That seems to be the/a problem with SpaceX as well.
The inputs for descent are different. You can almost mark the modes as they change - first, acquire and maintain a 0-AoA attitude, then start fiddling the throttle to come to a stop at some fixed low altitude, then, terminal guidance to translate to the landing pad, then acquire a fixed terminal descent rate until touchdown.
As anyone who has played Lander knows, the most fuel-efficient way to land is wait until the absolute last moment, then go to full throttle just high enough to stop before you hit. Just watching, it looks like it's plummeting out of control for a few seconds.
The exhaust changes color because they are adjusting the mixture ratio and flow rate to alter the thrust. The yellow and black smoke is where it goes very rich as the mixture ratio shifts. Throttling these types of engine is a very tricky matter, you can't just adjust the feed pressure up and down to anything you want because they are generally stable only over a narrow range. The Apollo descent engines were the pacing item in the moon landing because they had trouble getting the throttle to work of a a reasonable range of settings. As it was, it was not permissible to run something like the range between 10 and 40%.
Brett
I agree! They do have some reasons to celebrate but, they still have some work to do before they could call it a reliable system.
Randy Cuberly
-
I agree! They do have some reasons to celebrate but, they still have some work to do before they could call it a reliable system.
Randy Cuberly
Please, don't construe the above as a criticism. You ought to see the transient response of *my* thrust vector control system once it goes into saturation. Granted, my plant inertia is probably 10x theirs, and I have 1/2 ounce of thrust and bog-slow gimbals, but if you ever had an error large enough to see with the naked eye, ugly indeed.
There are significant limitation on the hardware they have to deal with leading to less than ideal transient response.
Brett
-
24 fps under the chute for the crew capsule. That will be the problem they will have to overcome. And 24 fps assumes the thing doesn't start swinging under the parachutes.
-
24 fps under the chute for the crew capsule. That will be the problem they will have to overcome. And 24 fps assumes the thing doesn't start swinging under the parachutes.
Having 3 chutes provides excellent damping.
Hitting at 24 FPS is clearly unacceptable without some sort of accomodation, An air bag is a workable idea, and given the lack of any consequential heat shield, seems practical. Adding deployable items is always a reliability concern, however.
Brett
-
remember that this rocket did not escape earths gravity..... it went straight up and only escaped our air...not traveles at 221,ooo miles per hour to escape the gravity and orbit like the space shuttle does...
-
remember that this rocket did not escape earths gravity..... it went straight up and only escaped our air...not traveles at 221,ooo miles per hour to escape the gravity and orbit like the space shuttle does...
Uhhh....I think you have an extra 1 in that number. More like 18 to 22,000 MPH.
Here's a little math to figure it out if you'd like! LL~ LL~ LL~
Mean orbital speed
For orbits with small eccentricity, the length of the orbit is close to that of a circular one, and the mean orbital speed can be approximated either from observations of the orbital period and the semimajor axis of its orbit, or from knowledge of the masses of the two bodies and the semimajor axis.[citation needed]
v_o \approx {2 \pi a \over T}v_o \approx \sqrt{\mu \over a}
where v is the orbital velocity, a is the length of the semimajor axis, T is the orbital period, and μ=GM is the standard gravitational parameter. Note that this is only an approximation that holds true when the orbiting body is of considerably lesser mass than the central one, and eccentricity is close to zero.
Taking into account the mass of the orbiting body,
v_o \approx \sqrt{G (m_1 + m_2) \over r}
where m1 is the mass of the orbiting body, m2 is the mass of the body being orbited, r is specifically the distance between the two bodies (which is the sum of the distances from each to the center of mass), and G is the gravitational constant. This is still a simplified version; it doesn't allow for elliptical orbits, but it does at least allow for bodies of similar masses.
When one of the masses is almost negligible compared to the other mass, as the case for Earth and Sun, one can approximate the previous formula to get:
v_o \approx \sqrt{\frac{GM}{r}}
or assuming r equal to the body's radius
v_o \approx \frac{v_e}{\sqrt{2}}
Where M is the (greater) mass around which this negligible mass or body is orbiting, and ve is the escape velocity.
For an object in an eccentric orbit orbiting a much larger body, the length of the orbit decreases with orbital eccentricity e, and is an ellipse. This can be used to obtain a more accurate estimate of the average orbital speed:
v_o = \frac{2\pi a}{T}\left[1-\frac{1}{4}e^2-\frac{3}{64}e^4 -\frac{5}{256}e^6 -\frac{175}{16384}e^8 - \dots \right] [2]
The mean orbital speed decreases with eccentricity.
-
remember that this rocket did not escape earths gravity..... it went straight up and only escaped our air...not traveles at 221,ooo miles per hour to escape the gravity and orbit like the space shuttle does...
The velocity for orbital flight is about 17,500 for a reasonable altitude, and it certainly doesn't escape the Earth's gravity. The gravity is what keeps it in orbit, no gravity, and you get a straight line. To escape the Earth completely, you need about 24500 miles an hour.
At any rate, no one seems to be claiming more than just a quickie vertical shot. It's not a technology that can easily be extended to orbital missions and I am sure that the people at Blue Origin know that. Re-usable single-stage to orbit rockets are hypothetically possible with very high technology and tiny payloads, but they aren't going to manage to come back and land as tail-sitters using rocket fuel. To do that you would have to carry heat shields and enough excess propellant to land all the way to orbit and back.
Brett
-
We have some incredibly intelligent and knowledgeable people on this forum. From rocket scientists to model builders, everyone brings something to the table known as Stunthanger. y1