Apollo and other re-entries
D. Liebenwurst
landing phase is control given to the pilots.
Didthe apollo capsules, and do the Soyuz capsules, use automated
re-entry, or is any of the control given to the pilots? Did Germini
and Mercury have automated re-entries?
Joe D.
news:o2pa4v8smacenbijl...@4ax.com...
>
> Didthe apollo capsules, and do the Soyuz capsules, use automated
> re-entry, or is any of the control given to the pilots? Did Germini
> and Mercury have automated re-entries?
>
While Mercury had automated re-entry, I think Gordon Cooper flew a fully
manual reentry due to the auto system failing. Scott Carpenter flew (after a
certain point) an essentially unguided reentry, since he totally ran out of
RCS fuel. That Carpenter survived shows one advantage of a capsule vs a
winged vehicle.
-- Joe D.
Henry Spencer
D. Liebenwurst <sp...@foo.org> wrote:
>OK, so the shuttles re-enter under automated guidance; only in the
>landing phase is control given to the pilots.
The pilots can fly the reentry -- it's demanding but possible. For
example, on STS-1, John Young took over control after he saw the early
reentry software doing things he didn't like. (Not bugs in the code, but
oversights in the spec.)
>Didthe apollo capsules, and do the Soyuz capsules, use automated
>re-entry, or is any of the control given to the pilots? Did Germini
>and Mercury have automated re-entries?
Same story: primary control is automatic but there was manual override.
Cooper had to fly a manual Mercury retrofire and reentry after his
automatic guidance system packed it in. Gemini had minor manual
participation even in normal reentries, I believe, when they were
experimenting with reentry guidance strategies. The Apollo designers had
to go to a significant effort to design flight instrumentation that could
show Apollo's complex reentry clearly enough to tell a pilot whether the
automation was screwing up, and/or guide him through flying it manually.
--
Faster, better, cheaper requires leadership, | Henry Spencer
not just management. | he...@spsystems.net
Mary Shafer
wrote:
> In article <o2pa4v8smacenbijl...@4ax.com>,
> D. Liebenwurst <sp...@foo.org> wrote:
> >OK, so the shuttles re-enter under automated guidance; only in the
> >landing phase is control given to the pilots.
>
> The pilots can fly the reentry -- it's demanding but possible. For
> example, on STS-1, John Young took over control after he saw the early
> reentry software doing things he didn't like. (Not bugs in the code, but
> oversights in the spec.)
No, he didn't. Subsequent flights had the energy management maneuvers
flown manually, but John just toughed it out. Fortunately the
stagnation point didn't move off the RCC nose cap, at least not long
enough to do any damage.
Cf Iliff and Shafer on Shuttle stability and control derivatives.
You'll see the time history of an STS-1 maneuver, followed by the time
history of an STS-2 maneuver. The first was automated, the second hand
flown. (If you don't find one with both authors, drop Shafer--one of
our three papers was given at a NASA conference and doesn't have a TM
version to be in the database.)
The reason for this was that the yawing moment due to yaw jet was, in
actuality, half the magnitude and the opposite sign from the predicted
value. It's because the yaw jet was firing into an unpressurized volume
of separated flow, as I remember. Actually, the FCS was remarkably
robust, considering.
Mary
--
Mary Shafer mil...@qnet.com
Retired Aerospace Research Engineer
"A MiG at your six is better than no MiG at all."
Anonymous US fighter pilot
Duncan Munro
Soyuz can do it either way, or it can re-enter with no guidance.
Duncan
Chris Williams
wrote:
>Same story: primary control is automatic but there was manual override.
>Cooper had to fly a manual Mercury retrofire and reentry after his
>automatic guidance system packed it in.
Gemini and Apollo I understand, but what was manual about a Mercury
re-entry? I understood that the capsule was ballistic and thus could
not be steered. Was it just a matter of attitude control?
Chris
D. Liebenwurst
wrote:
No guidance? I'm not sure what you mean here. Surely the capsule
would have to manuever just to keep the heat shield pointed in the
right direction.
>Duncan
GB
all automatic. He didn't need to touch a thing, just monitor in case. Fully
manual was there for him though.
Also, after a bit more research on the descent trajectory, it was
interesting that the standard profile for a Lunar mission re-entry involved
going back up for a while.
GB.
Henry Spencer
D. Liebenwurst <sp...@foo.org> wrote:
>>Soyuz can do it either way, or it can re-enter with no guidance.
>
>No guidance? I'm not sure what you mean here. Surely the capsule
>would have to manuever just to keep the heat shield pointed in the
>right direction.
Like the US capsules, it is aerodynamically stable in the right orientation.
Kevin Willoughby
The Soyuz reentry capsule is spherical. If its attitude is off by a
little bit, it isn't a big thing.
--
Kevin Willoughby kevinwi...@scispace.org.invalid
What gets measured gets done. -- David Patterson
Greg D. Moore (Strider)
"Kevin Willoughby" <ke...@scispace.org.invalid> wrote in message
news:MPG.18af9ef11...@news.rcn.com...
> D. Liebenwurst said:
> > On Sun, 09 Feb 2003 00:50:36 GMT, Duncan Munro <dunm...@shaw.ca>
> > wrote:
> > >Soyuz can do it either way, or it can re-enter with no guidance.
> >
> > No guidance? I'm not sure what you mean here. Surely the capsule
> > would have to manuever just to keep the heat shield pointed in the
> > right direction.
>
> The Soyuz reentry capsule is spherical. If its attitude is off by a
> little bit, it isn't a big thing.
Umm, not quite, it's rather flatter on one side than the others.
http://www.energia.ru/energia/iss/soyuz-tma/im/soyuz-tma_lay-outs.jpg
Darren J Longhorn
<ke...@scispace.org.invalid> wrote:
>The Soyuz reentry capsule is spherical. If its attitude is off by a
>little bit, it isn't a big thing.
Oh no it isn't...
http://www.russianspaceweb.com/soyuz.html
--
Darren J Longhorn
It's all faked, I tell you, all of it!
You want proof? I'll give you your stinkin' proof...
http://www.geocities.com/darrenlonghorn/proof/nasa2.jpg
Doug...
ke...@scispace.org.invalid says...
> D. Liebenwurst said:
> > On Sun, 09 Feb 2003 00:50:36 GMT, Duncan Munro <dunm...@shaw.ca>
> > wrote:
> > >Soyuz can do it either way, or it can re-enter with no guidance.
> >
> > No guidance? I'm not sure what you mean here. Surely the capsule
> > would have to manuever just to keep the heat shield pointed in the
> > right direction.
>
> The Soyuz reentry capsule is spherical. If its attitude is off by a
> little bit, it isn't a big thing.
You're thinking of the Vostok/Voskhod entry capsules, Kevin. Those were
essentially spherical, with only the cg to keep the window out of the
hottest part of the entry heating. The Soyuz entry capsule is bell-
shaped. Interestingly, it is *very* close to the same shape as the
General Electric design proposal for Apollo.
Doug Van Dorn
dvan...@mn.rr.com
Henry Spencer
GB <geo...@bigpond.com> wrote:
>Also, after a bit more research on the descent trajectory, it was
>interesting that the standard profile for a Lunar mission re-entry involved
>going back up for a while.
Careful, there are errors in some accounts of this. Only the Zonds really
flew "skip" trajectories, actually rising out of the atmosphere and coming
down again; Apollo sometimes rose a bit but not very much. An Apollo
reentry was basically a long, flat high-altitude glide, using aerodynamic
lift to hold the capsule down in the atmosphere.
Apollo was originally going to have skip trajectories as an option, but
the skip's ability to stretch the reentry out became less crucial as
design constraints changed... and neither of the backup reentry-guidance
approaches could handle a skip reentry, so it was eventually dropped.
Henry Spencer
Chris Williams <vontri...@hotmailthemick.com> wrote:
>>Cooper had to fly a manual Mercury retrofire and reentry after his
>>automatic guidance system packed it in.
>
>Gemini and Apollo I understand, but what was manual about a Mercury
>re-entry? I understood that the capsule was ballistic and thus could
>not be steered. Was it just a matter of attitude control?
Right. It became pretty academic once drag built up, since the capsule
was stable in the right orientation, but early on one had to do attitude
control.
Henry Spencer
Kevin Willoughby <kevinwi...@acm.org.nospam.invalid> wrote:
>> >Soyuz can do it either way, or it can re-enter with no guidance.
>> No guidance? I'm not sure what you mean here. Surely the capsule
>> would have to manuever just to keep the heat shield pointed in the
>> right direction.
>
>The Soyuz reentry capsule is spherical. If its attitude is off by a
>little bit, it isn't a big thing.
Nope. Vostok and Voskhod were spherical, making purely ballistic reentries
like Mercury. Soyuz is sort of acorn-shaped, and makes a semiballistic
lifting reentry like Apollo.
However, like Apollo, it is aerodynamically stable in its reentry
orientation, so there is no need for guidance once drag builds up, and in
a pinch you can skip it even before that.
Kevin Willoughby
> On Sun, 9 Feb 2003 16:48:53 -0500, Kevin Willoughby
> <ke...@scispace.org.invalid> wrote:
>
> >The Soyuz reentry capsule is spherical. If its attitude is off by a
> >little bit, it isn't a big thing.
>
> Oh no it isn't...
D'oh! Soyuz isn't Vostok. I knew that, honest.
sigh...
Phil Fraering
>Careful, there are errors in some accounts of this. Only the Zonds really
>flew "skip" trajectories, actually rising out of the atmosphere and coming
>down again; Apollo sometimes rose a bit but not very much. An Apollo
>reentry was basically a long, flat high-altitude glide, using aerodynamic
>lift to hold the capsule down in the atmosphere.
_Down_ in the atmosphere?
I thought it was still flying a lifting reentry?
--
Phil Fraering "One day, Pinky, A MOUSE shall rule, and it is the
p...@globalreach.net humans who will be forced to endure these humiliating
diversions!"
"You mean like Orlando, Brain?"
OM
>he...@spsystems.net (Henry Spencer) writes:
>
>>Careful, there are errors in some accounts of this. Only the Zonds really
>>flew "skip" trajectories, actually rising out of the atmosphere and coming
>>down again; Apollo sometimes rose a bit but not very much. An Apollo
>>reentry was basically a long, flat high-altitude glide, using aerodynamic
>>lift to hold the capsule down in the atmosphere.
>
>_Down_ in the atmosphere?
>
>I thought it was still flying a lifting reentry?
...It was. Remember, they had to account for the possibility of
skipping off the atmosphere and back out into space. The offset C/G
allowed for adjusting the lift so as to allow for that capability.
OM
--
"No bastard ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb bastard die for his country." | Human O-Ring Society
- General George S. Patton, Jr
Henry Spencer
Phil Fraering <pgf@AUTO> wrote:
>>...Apollo sometimes rose a bit but not very much. An Apollo
>>reentry was basically a long, flat high-altitude glide, using aerodynamic
>>lift to hold the capsule down in the atmosphere.
>
>_Down_ in the atmosphere?
>I thought it was still flying a lifting reentry?
It was, but with the lift vector pointed *down* most of the time.
Dave Tenney
"Henry Spencer" <he...@spsystems.net> wrote in message
news:HA3p7...@spsystems.net...
I seem to remember reading (I forget where, sorry) that the auto system
would initiate a roll when the 0.5g relay closed. The theory being to
equalize the heating of the capsule skin during reentry. The roll would then
be terminated at some point before drogue deployment.
Does anyone know where I might have got that (other than out of a beer
bottle?)
--Dave--
Henry Spencer
Dave Tenney <dte...@mail.smu.edu> wrote:
>[Mercury]
>I seem to remember reading (I forget where, sorry) that the auto system
>would initiate a roll when the 0.5g relay closed. The theory being to
>equalize the heating of the capsule skin during reentry.
0.05g relay, actually. Glenn had to activate it manually, because its
operation was keyed to retropack jettison.
The motivation for the roll was not so much thermal, I believe, as to zero
out the effects of lift caused by any center-of-mass offset. For Mercury
this offset was intended to be zero, but it might not be exactly that, and
a stable attitude would have let trajectory errors from the resulting lift
build up.
Some of the Gemini flights -- which had a deliberately non-zero offset --
flew an actively-controlled lifting trajectory until they intersected a
suitable pure-ballistic trajectory, and then set up a roll to follow the
ballistic trajectory.
Dave Tenney
<snip>
> 0.05g relay, actually. Glenn had to activate it manually, because its
> operation was keyed to retropack jettison.
>
> The motivation for the roll was not so much thermal, I believe, as to zero
> out the effects of lift caused by any center-of-mass offset. For Mercury
> this offset was intended to be zero, but it might not be exactly that, and
> a stable attitude would have let trajectory errors from the resulting lift
> build up.
>
> Some of the Gemini flights -- which had a deliberately non-zero offset --
> flew an actively-controlled lifting trajectory until they intersected a
> suitable pure-ballistic trajectory, and then set up a roll to follow the
> ballistic trajectory.
> --
> Faster, better, cheaper requires leadership, | Henry Spencer
> not just management. |
he...@spsystems.net
Yeah, that makes more sense, since if your entry attitude was correct and
the center of mass was in line with the trajectory the heating should be
even (equal air friction on all sides parallel to the direction of travel
right?) And of course I meant 0.05g...
Now where did I put that that other zero anyway?
--Dave--
Rick DeNatale
<he...@spsystems.net> wrote:
> In article <o7fmh-...@lungold.globalreach.net>,
> Phil Fraering <pgf@AUTO> wrote:
> >>...Apollo sometimes rose a bit but not very much. An Apollo
> >>reentry was basically a long, flat high-altitude glide, using aerodynamic
> >>lift to hold the capsule down in the atmosphere.
> >
> >_Down_ in the atmosphere?
> >I thought it was still flying a lifting reentry?
>
> It was, but with the lift vector pointed *down* most of the time.
Actually I'd think that the lift vector pointed mostly up (this is
almost by the definition of lift). This lift force would decelerate the
rentry, but wouldn't result in a net upward velocity. The off-center
lift of the Apollo capsule gave some control in pointing the lift
vector relative to the trajectory.
A glider wing provides upward lift, but in the absence of an updraft, a
glider will descend, albeit more slowly than a liftless rock.
Henry Spencer
Rick DeNatale <dena...@ctc.net> wrote:
>> >_Down_ in the atmosphere?
>> >I thought it was still flying a lifting reentry?
>> It was, but with the lift vector pointed *down* most of the time.
>
>Actually I'd think that the lift vector pointed mostly up (this is
>almost by the definition of lift).
Nope. The definition of lift is aerodynamic force at right angles to the
airflow. (Aerodynamic force in line with the airflow is drag.) You can
point the lift vector any way you want by just rolling the aircraft; an
aircraft makes a tight turn by pointing its lift vector more or less
horizontally.
The Apollo reentry started out with lift pointed up, essentially to pull
the capsule out of its descent, but then (with fairly careful timing)
switched to pointing it down, to keep the capsule within the atmosphere.
>A glider wing provides upward lift, but in the absence of an updraft, a
>glider will descend, albeit more slowly than a liftless rock.
You're forgetting "centrifugal lift". The Apollo capsule started out
moving considerably faster than orbital velocity, so its natural tendency
was not to fall down, but to fall *up*, as the curved Earth dropped out
from under it faster than gravity could pull it down. Pointing the lift
vector down fought that, holding it within the atmosphere while velocity
slowly bled off.
Robert Conley
Mercury used a purely ballistic re-entry. The automatic thrusters kept
it oriented properly after retrofire and after .05 Gs of deceleration
was registered the capsule was put into a spin to stabilize it during
re-entry. Gordon Cooper had to do all this manually after the
automatic controller failed.
Gemini had an offset center of gravity which gave the capsule a cross
range of 54 nautical miles and a downrange of 300 miles. Gemini
re-entry were done by either spinning capsules several degrees per
minutes to produce no lift and then stopping the spine in a particular
roll position to adjust the landing point. Other missions did a
contanst bank where the capsule was held in a particular roll position
throughout re-entry.
Gemini 3 missed because the actual Lift over drag L/D was a lot lower
than expected. Capsule landed 60 n.m. from target
Gemini 4 the computer crapped out so the re-entry had to be flow
manually in open loop mode (closed loop meaning the computer helped
the astronaut in precision control of the thrusters). Culminative
errors caused the capsule to land 40 n.m from target.
Gemini 5 land 91 n.m. off target due the fact the programmers of the
re-entry routines forget to take in account the earth rotates.
Gemini 6 was the first to have it all put together and landed 7 n.m.
from target
Gemini 7 was 6.4 n.m of target thus Borman won his bet with Schirra as
to who could land closer.
Gemini 8 was forced to come down early and landed 1.4 n.m. from target
Gemini 9 was .38 n.m Gemini X was 3.4 Gemini XI was 2.65 and Gemini
XII was 2.6
Gemini XI's re-entry was flown completely on automatic control and
used the rolling re-entry logic.
My Gemini model with Orbiter sim allows you to fly the Gemini re-entry
accurately.
Apollo also had a offset center of gravity and did a double dip
re-entry. The capsule dipped and bled off speed and rose up again.
Then it dipped again this time completing the re-entry. This was to
prevent overheating of the heat shield and capsule.
The Soyuz has the same capability as the Apollo and in two different
Zond mission the Soviets successfully pulled off a double dip re-entry
using the Soyuz capsule.
Vostok (and Voskhod) had a simple sphere for a capsule and the center
of gravity was designed so that the capsule oriented properly doing
re-entry so that the chutes could deploy properly afterwards.
Rob Conley
http://www.orbitersim.com
http://www.alltel.net/~estar/orbiter.html
Phil Fraering
>In article <o7fmh-...@lungold.globalreach.net>,
>Phil Fraering <pgf@AUTO> wrote:
>>>...Apollo sometimes rose a bit but not very much. An Apollo
>>>reentry was basically a long, flat high-altitude glide, using aerodynamic
>>>lift to hold the capsule down in the atmosphere.
>>
>>_Down_ in the atmosphere?
>>I thought it was still flying a lifting reentry?
>It was, but with the lift vector pointed *down* most of the time.
I always thought it was pointed up, to keep it from hitting denser
regions of the atmosphere too fast, and to keep g-forces to within
acceptable limits.
Henry Spencer
Phil Fraering <pgf@AUTO> wrote:
>>>I thought it was still flying a lifting reentry?
>>It was, but with the lift vector pointed *down* most of the time.
>
>I always thought it was pointed up, to keep it from hitting denser
>regions of the atmosphere too fast, and to keep g-forces to within
>acceptable limits.
Once velocity falls below orbital, yes, that becomes the driving issue.
That was not Apollo's main problem. (Although "most" may have been
overstating things a bit.)
Rick DeNatale
<he...@spsystems.net> wrote:
> In article <b393i-...@lungold.globalreach.net>,
> Phil Fraering <pgf@AUTO> wrote:
> >>>I thought it was still flying a lifting reentry?
> >>It was, but with the lift vector pointed *down* most of the time.
> >
> >I always thought it was pointed up, to keep it from hitting denser
> >regions of the atmosphere too fast, and to keep g-forces to within
> >acceptable limits.
>
> Once velocity falls below orbital, yes, that becomes the driving issue.
> That was not Apollo's main problem.
Henry, wouldn't pointing the lift vector up increase rather than
decrease g-force? It would seem that if the lft force were acting up
deacceleration would be higher. Or do I have another misconception?
Henry Spencer
Rick DeNatale <dena...@ctc.net> wrote:
>> >I always thought it was pointed up, to keep it from hitting denser
>> >regions of the atmosphere too fast, and to keep g-forces to within
>> >acceptable limits.
>
>Henry, wouldn't pointing the lift vector up increase rather than
>decrease g-force?
Nope. The g-force is entirely produced by aerodynamic forces -- it is
independent of which way those forces are pointed with respect to the
outside world. (G-force, pressing you into your seat or whatever, has to
be produced by something that accelerates/decelerates the seat but not
you. Gravity attracts both equally.)
The importance of pointing the lift vector up, when you are at below
orbital velocity, is less immediate: it keeps you higher up, in thinner
air, where forces are smaller and you thus decelerate more gradually.
A purely ballistic trajectory, with no lift, loses altitude too quickly
even if it starts out pretty nearly horizontal.
D. Liebenwurst
wrote:
>In article <160220031132595033%dena...@ctc.net>,
Speaking of G-forces, I heard the Apollo astronauts were subjected to
forces up to 8 G's. The shuttle keeps it below three, but the
astronauts interviewed over the past two weeks make it sound like it
was a little over 1 G.
Henry Spencer
D. Liebenwurst <sp...@foo.org> wrote:
>Speaking of G-forces, I heard the Apollo astronauts were subjected to
Not that bad, not in a normal mission. (Abort cases are another story
entirely.) Launch acceleration peaks at about 4G, just before S-IC burnout.
Reentry deceleration averages about 4G, although I think there is a brief
peak higher than that. It's not hard to design a somewhat larger capsule
to limit reentry deceleration to about 2.5G.
>The shuttle keeps it below three, but the
>astronauts interviewed over the past two weeks make it sound like it
>was a little over 1 G.
Shuttle ascent is limited to 3G. It's the descent that is normally not
much over 1G.
Rick DeNatale
<he...@spsystems.net> wrote:
> In article <160220031132595033%dena...@ctc.net>,
> Rick DeNatale <dena...@ctc.net> wrote:
> >Henry, wouldn't pointing the lift vector up increase rather than
> >decrease g-force?
>
> Nope. The g-force is entirely produced by aerodynamic forces -- it is
> independent of which way those forces are pointed with respect to the
> outside world. (G-force, pressing you into your seat or whatever, has to
> be produced by something that accelerates/decelerates the seat but not
> you. Gravity attracts both equally.)
Of course that's besides the point, since the lift is also an
aerodynamic force.
> The importance of pointing the lift vector up, when you are at below
> orbital velocity, is less immediate: it keeps you higher up, in thinner
> air, where forces are smaller and you thus decelerate more gradually.
> A purely ballistic trajectory, with no lift, loses altitude too quickly
> even if it starts out pretty nearly horizontal.
And that was my misconception I guess. I was thinking of the reentry as
being steeper, so that "up" was at less of an angle to normal to the
crews backs.