Dynamic re-entry profile ?

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Adam Darren - 27 Sep 2003 06:19 GMT

Right now, the properties of the pre-determined re-entry profile are well
known and the shuttle's guidance computer is well programmed to handle it,
allowing shuttle to de-orbit at the right time and reach the runway vicinity
at the right altitude/speed. They even know prior to de-orbit burn the target
runway. Fairly routine stuff.

Ok, lets say that there was a problem with tiles and that they decided to
attempt a very different re-entry profile to protect the damaged side (at the
expense of other areas). Could the re-entry program be modified with a new
re-entry profile while the shuttle is in orbit ?

Could the guidance computers be programmed to perform the initial/different
re-entry which would bring the shuttle to a random location at a specific
altitude and more or less random speed, at which point ground could decide
which runway to target and re-load the computers with the necessary info to
reach that runway ?

Or are time constraints such that they would really need to program the full
re-entry in advance without any time to change anything once re-entry
interface has been reached ?

Is knowledge of re-entry aerodynamics such that NASA could quickly simulate a
very different re-entry profile yielding information that would allow NASA to
program the guidance computers to de-orbit at the right time and perform
whatever manoeuvers (skips, turns etc) and bring the shuttle out of re-entry
interface at the right location and altitude to allow landing at the right
runway ?

Reply to this Message

David Findlay - 27 Sep 2003 06:59 GMT

> Ok, lets say that there was a problem with tiles and that they decided to
> attempt a very different re-entry profile to protect the damaged side (at
> the expense of other areas). Could the re-entry program be modified with a
> new re-entry profile while the shuttle is in orbit ?

Well for a start, they already fly the best profile available, so even if
you could reprogram inflight, there is nothing better to run.

> Could the guidance computers be programmed to perform the
> initial/different re-entry which would bring the shuttle to a random
> location at a specific altitude and more or less random speed, at which
> point ground could decide which runway to target and re-load the computers
> with the necessary info to reach that runway ?

I don't think so, IIRC it's one program that does the whole approach. You
could likely fly manual though. Thanks,

David

Reply to this Message

Hallerb - 27 Sep 2003 13:10 GMT

>> Ok, lets say that there was a problem with tiles and that they decided to
>> attempt a very different re-entry profile to protect the damaged side (at
>> the expense of other areas).

>Well for a start, they already fly the best profile available, so even if
>you could reprogram inflight, there is nothing better to run.

Not true. Columbia was flying a hot profile to attemot to warm its tires.after
its long cold soak in space.

Without the pictures we dont have enough info to ever know exactly if the crew
could of been saved.

Reply to this Message

Lynndel Humphreys - 27 Sep 2003 13:33 GMT

Not sure but I seem to recall someone saying Orlando International had the
capability to allow the shuttle to land. The most easterly runway is
extremely long I assume in case an unusually large alligator, 60 feet or
so, decided to sun itself on the shuttle landing strip and refused to leave.

Reply to this Message

Jon Berndt - 27 Sep 2003 13:53 GMT

"Adam Darren" <adarren@interns.dell.com> wrote in message

> Ok, lets say that there was a problem with tiles and that they decided to
> attempt a very different re-entry profile to protect the damaged side (at the
> expense of other areas).

I don't believe there's really much of a predictable capability to do this;
the black side of the orbiter gets hot - the grey areas get really hot, and
the white areas aren't supposed to get very hot. ;-) Aerodynamics, control,
and thermal constraints dictate the attitude the orbiter flies at during
entry. "Protecting" a damaged area - even if theoretically possible - would
likely involve flying in an un-trimmed state and require constant jet
firings and also possibly put other areas of the vehicle over their
allowable design temperatures and creating more (and possibly worse)
problems.

> Could the re-entry program be modified with a new
> re-entry profile while the shuttle is in orbit ?

There are three parameters that are very important at EI (entry interface):
energy (altitude and speed), REI (range at entry interface), and the angle
at EI. REI and the angle at EI have to be within a specific range and are
dependent on many things including vehicle weight, etc. The shuttle's entry
conditions have been adjusted over the years, as I recall, to result in the
most benign entry possible. There has been some discussion about decresing
the angle at EI *slightly* and increasing the REI *slightly* in order to
provide a lower *peak* temperature, but that would result in greater tile
backface temperatures - there's always a tradeoff. I have seen other papers
that purport to lower the temps even further, but they are only theoretical
and have not been tested or evaluated in any way.

> Could the guidance computers be programmed to perform the initial/different
> re-entry which would bring the shuttle to a random location at a specific
> altitude and more or less random speed, at which point ground could decide
> which runway to target and re-load the computers with the necessary info to
> reach that runway ?

If I am not mistaken, if the drag was greater than expected and the orbiter
for some reason could not make the planned site, the orbiter could be
retargeted to another site that was reacheable. The crew would need to know
exactly which site was best for them, though, and potential landing sites
are not that common. I think with upcoming software releases there are about
90 runways that will be in the orbiters database. Selecting the right one
will be made easier with software that I am involved in testing right now.
See http://www.spacecoretech.org/coretech2002/ssa.html. There are some
papers hosted there that explain the capabilities of SAFM:

1) Onboard Determination of Vehicle Glide Capability for Shuttle Abort
Flight Management (SAFM)

2) Shuttle Flight Abort Management (SAFM) - Application Overview

This new application is possible due to the capabilities provided as part of
the CAU program. [Another poster in a separate thread has claimed that the
MEDS displays and/or CAU is somehow responsible or related to the demise of
Columbia because of "improperly spent funds", but I find this claim to be
without merit and misguided]. You might find the above documents to be an
interesting read.

Jon

Reply to this Message

Craig Fink - 29 Sep 2003 13:55 GMT

> "Adam Darren" <adarren@interns.dell.com> wrote in message
>
[quoted text clipped - 31 lines]
> papers that purport to lower the temps even further, but they are only
> theoretical and have not been tested or evaluated in any way.

They could reduce the EI flight path angle further and pick a little extra
payload by changing the initial roll at EI to 180 degrees. Essentially,
grabbing a hold of the atmosphere and pulling themselves deeper into it.
Payload would be slightly increased because the deorbit burn delta-V
requirements would be reduced.

Additionally, if they had realtime heating sensors in the wing, there is
probably a small window where the Orbiter could abort the entry. Too much
heat in the wing, roll to heads up, raise perigee slightly and apply a
patch to the Orbiter and try again. Although this might come at the cost of
a little payload, as more OMS/RCS FPR would be required.

Craig Fink

Reply to this Message

Space Forum / Shuttle / September 2003

Dynamic re-entry profile ?