News:


  • April 17, 2024, 11:36:06 PM

Login with username, password and session length

Author Topic: Rocket science  (Read 4574 times)

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12808
Rocket science
« on: November 24, 2015, 10:44:29 AM »
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline FLOYD CARTER

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4458
    • owner
Re: Rocket science
« Reply #1 on: November 24, 2015, 11:30:28 AM »
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?
89 years, but still going (sort of)
AMA #796  SAM #188  LSF #020

Offline FLOYD CARTER

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4458
    • owner
Re: Rocket science
« Reply #2 on: November 24, 2015, 11:30:28 AM »
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?
89 years, but still going (sort of)
AMA #796  SAM #188  LSF #020

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12808
Re: Rocket science
« Reply #3 on: November 24, 2015, 11:33:22 AM »
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.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Randy Cuberly

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3674
Re: Rocket science
« Reply #4 on: November 24, 2015, 12:20:33 PM »
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
Randy Cuberly
Tucson, AZ

Offline Motorman

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3257
Re: Rocket science
« Reply #5 on: November 24, 2015, 01:44:55 PM »
Ah, wasn't that all computer generated animation?


MM

Offline RknRusty

  • 2019 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2689
    • My Tube channel
Re: Rocket science
« Reply #6 on: November 24, 2015, 04:09:17 PM »
DON'T PANIC!
Rusty Knowlton
... and never Ever think about how good you are at something...
while you're doing it!

Jackson Flyers Association (a.k.a. The Wildcat Rangers(C/L))- Fort Jackson, SC
Metrolina Control Line Society (MCLS) - Huntersville, NC - The Carolina Gang
Congaree Flyers - Gaston, SC -  http://www.congareeflyer.com
www.coxengineforum.com

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12808
Re: Rocket science
« Reply #7 on: November 24, 2015, 05:30:00 PM »
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.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Steve Fitton

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2272
Re: Rocket science
« Reply #8 on: November 24, 2015, 06:32:33 PM »
I don't see how the capsule can land soft enough with just a parachute and no braking rockets.
Steve

Offline Motorman

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3257
Re: Rocket science
« Reply #9 on: November 24, 2015, 06:55:06 PM »
It didn't show how it re-enters the atmosphere. It went from outer space to parachute, you skipped a step there.


MM


Offline Steve Helmick

  • AMA Member and supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 9933
Re: Rocket science
« Reply #11 on: November 24, 2015, 07:17:02 PM »
At least it's Internal Combustion powered, and not using some electron mumbo-jumbo, Jimbo.  S?P Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13732
Re: Rocket science
« Reply #12 on: November 24, 2015, 08:19:31 PM »
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

Offline Randy Cuberly

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3674
Re: Rocket science
« Reply #13 on: November 24, 2015, 10:57:23 PM »
     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
Randy Cuberly
Tucson, AZ

Offline mike londke

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1470
Re: Rocket science
« Reply #14 on: November 24, 2015, 11:30:14 PM »
Ah, wasn't that all computer generated animation?


MM
A simple search of the web would have told you it is in fact real.
AMA 48913  USPA D-19580  NRA Life Member  MI State Record Holder 50 way Freefall Formation Skydive  "Don't let the planet sneak up on you"

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13732
Re: Rocket science
« Reply #15 on: November 25, 2015, 12:19:19 PM »
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

Offline Randy Cuberly

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3674
Re: Rocket science
« Reply #16 on: November 25, 2015, 02:49:07 PM »
   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
Randy Cuberly
Tucson, AZ

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13732
Re: Rocket science
« Reply #17 on: November 25, 2015, 05:08:42 PM »
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

Offline Steve Fitton

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2272
Re: Rocket science
« Reply #18 on: November 26, 2015, 06:35:11 AM »
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.
Steve

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13732
Re: Rocket science
« Reply #19 on: November 26, 2015, 12:56:34 PM »
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

Offline jim gilmore

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1216
Re: Rocket science
« Reply #20 on: November 26, 2015, 01:19:15 PM »
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...

Offline Randy Cuberly

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3674
Re: Rocket science
« Reply #21 on: November 26, 2015, 01:59:02 PM »
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.
Randy Cuberly
Tucson, AZ

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13732
Re: Rocket science
« Reply #22 on: November 26, 2015, 09:35:21 PM »
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

Offline Dick Pacini

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1629
Re: Rocket science
« Reply #23 on: November 26, 2015, 10:54:29 PM »
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
AMA 62221

Once, twice, three times a lady.  Four times and she does it for a living.  "You want me on that wall.  You need me on that wall."


Advertise Here
Tags:
 


Advertise Here