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Author Topic:   Manual re-entry on Mercury orbital missions

Posts: 124
Registered: Jul 2016

posted 11-28-2017 06:28 AM     Click Here to See the Profile for Jim_Voce   Click Here to Email Jim_Voce     Edit/Delete Message   Reply w/Quote
For the Mercury orbital missions, did the astronauts perform complete manual control for reentry or only partial control? In Gordon Cooper's (MA-9) case, he had to manage all aspects of deorbiting and reentry I believe.

And also, did Alan Shepard (MR-3) and Gus Grissom (MR-4) perform any manual functions at all during their suborbital flights?


Posts: 4060
From: Sierra Vista, Arizona
Registered: Nov 1999

posted 11-28-2017 06:39 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Lots of questions... Many of the answers you seek can be located in the associated mission reports.


Posts: 2355
From: U.K.
Registered: Jul 2009

posted 11-28-2017 08:11 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Certainly in the case of Carpenter's flight there was partial control as detailed in my previous post here -
The countdown given by Shepard reached zero. Nothing happened. At this point everyone was expecting the automatic sequencer to fire the three retro-rockets.

Carpenter hit the manual override button. And again – nothing happened. There was a two second delay before the rockets actually fired producing in the cabin a puff of acrid smoke probably caused by a short circuit in the firing mechanism. This delay contributed some 15 to 20 miles to the overshoot on landing.

When the rockets fired in their ripple pattern they did not produce the kick that Carpenter was expecting. This loss of the expected thrust added another 60 miles.

The remaining 170 or so miles came as a result of a misalignment during retrofire. Not in the vital pitch angle but in yaw. When the rockets fired the capsule was slanted about 25 degrees off to the right. As retrofire progressed Carpenter gradually brought this back to zero, but because the rockets did not fire in an absolutely straight line down the flight path they lost effectiveness.

All three elements added up to 250 miles over the expected landing point.


Posts: 124
Registered: Jul 2016

posted 11-28-2017 10:52 PM     Click Here to See the Profile for Jim_Voce   Click Here to Email Jim_Voce     Edit/Delete Message   Reply w/Quote
Thank you for the fascinating details on Carpenter.

It has always been stated that Carpenter was blamed for three things:

  • Using too much fuel to chase Glenn's "fireflies"
  • Not monitoring his fuel consumption
  • Firing his retro-rockets too late
As I recall, it was concluded that there was a flaw in the fuel control that had the system expending too much fuel. So every time that Carpenter used it, the fuel consumption was much greater than expected. Is this correct?

By what you are saying, Carpenter was not at fault for firing his retro-rockets late — there was a technical problem and the system sputtered rather than fired. If so, then it appears that Carpenter is at fault really for just one thing and that is not monitoring his fuel consumption. Is this correct?


Posts: 232
From: Perth, Western Australia
Registered: Apr 2015

posted 11-29-2017 01:29 AM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
These subjects for Carpenter's flight are covered in both his and Chris Kraft's Oral History Project interviews.


Posts: 2355
From: U.K.
Registered: Jul 2009

posted 11-29-2017 01:44 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
I hope this answers some of your questions -
First, the fuel management problem. Wolfe talks about Carpenter being unaware "...until the third and last orbit" that he was short of fuel having received warnings from "...several Capcoms" to start conserving during the second orbit. Carpenter himself, barely half way round on his first orbit, is the first to mention that the need to orientate the capsule to meet the requirements of some of his experiments had caused him to use more fuel than was expected.

At the end of this first orbit Carpenter is already discussing ways of conserving his remaining supplies with the ground and by the beginning of his third orbit the message from the ground was to the effect that they were reasonably happy with the measures taken and were content for the flight to continue for its planned duration. Incidentally, it is worth recording at this stage that Glenn on his flight also received a warning about the rate he was using fuel and was told to allow his capsule to drift.

Some of the blame is readily accepted by Carpenter. He himself said after the mission that "...the spectacular novelty of the view from space challenged me to make the most of my opportunity and lured me into an unwise expenditure of fuel early in the flight." Then there were times when the fly-by-wire high thrust units were accidentally activated during some manoeuvres. (Fly-by-wire was the system used when the astronauts operated the manual control system but depleted automatic fuel supplies.) This is translated in the official report as "...pilot deviated from planned procedures."

Set against this must be added the fact that he was given, as part of the flight plan, a greater amount of manual control tasks to perform than previously attempted, some of which necessitated a frequent return to orbital attitudes. For these manoeuvres the automatic system was used consuming more fuel than was strictly necessary. Carpenter again acknowledged this stating that the experimental part of the mission consumed "fuel or time." What he meant by this was that the economical way to proceed was to nudge the capsule towards the desired attitude with a short puff from the control jets and then allow it to drift into position. This took time.

In order to keep up with the flight plan, Carpenter felt it necessary to drive the capsule on the thrusters all the way, making the manoeuvring faster but less efficient in the use of his fuel. Perhaps he was the first astronaut to find that the planners perception of a reasonable work load did not match the feasibility of operational requirements.

Time Comment Fuel Remaining
  Auto Manual
00:05:09 Turnaround completed using just 1·4 lb of the 4 lb allocated.  
00:12:00 to 00:45:00 During this period Carpenter tracked Atlas booster, took photographs and positioned capsule for star observations  
00:48:08 Oh dear! I've used too much fuel. Recorded on onboard tape machine following manoeuvres for MIT photographs and aligning capsule. 75 100
01:02:46 to 01:28:00 After a period of drifting flight manoeuvred capsule by body movements. Then orientated to observe sunrise and track snowflakes. 69 69
01:34:37 A little ahead on fuel consumption. Fuel quantity light is on. A warning light flashed on the instrument panel when quantity remaining reached 65%. 62 68
01:37:38 Everything looks good down here except your fuel useage. You better watch that for a bit. Cape.  
01:50:15 MCC is worried about your auto fuel and manual fuel consumption. They recommend that you try to conserve your fuel. Canary.

Roger. Tell them I'm concerned also. I will try and conserve fuel.

01:55:08 The only thing to report regarding the flight plan is that levels are lower than expected. I expended my extra fuel in trying to orient after night side. I think this is due to conflicting requirements of the flight plan. I should have taken time to orient and then work with other items. To Kano. 51 69
02:00:06 In reply to query from Kano about greater than expected fuel useage – I expended it on – by manual and fly-by-wire thrusters operation on the dark side and just approaching sunrise. I think that I can cut down the fuel consumption considerably on the second and third orbits.  
02:06:25 In response to query from Zanzibar about the intention to use fly-by-wire – I think that the fact that I'm low on fuel dictates that I stay on auto as long as the fuel consumption on automatic is not too excessive. 51 69
02:07:55 The Indian Ocean tracking ship passes on a message from the Cape to conserve fuel, adding that it had monitored the conversation with Zanzibar and understood the situation.  
02:08:47 to 02:26:50 Carpenter investigates a possible difficulty with the automatic control system, checking both thrusters and the ability of the gyros to hold zero rates.  
02:27:47 We suggest you go to manual at this point and preserve your auto fuel. Muchea 45 70
02:29:24 Cape informs that if we don't stay on manual for quite a spell here we'll probably have to end this orbit. Muchea  
02:43:51 Fuel is... a little ahead of schedule. To Canton. 45 64
02:50:45 Do you have an auto fuel warning light? Hawaii.

Carpenter responds that he reported it a long time ago and that it is now covered with tape.

03:00:15 General Kraft is still somewhat concerned about auto fuel. Use as little auto ... use no auto fuel unless you have to prior to retro-sequence. California 45 50
03:11:36 Replying to a query about drifting flight, Carpenter says that if he is going to save fuel for retro-sequence he had better start again.  
03:14:27 We're still fairly happy with your fuel state now. Don't let ... we'd like for you not to let either get down below 40 percent. Cape. 45 42
 Fuel reserves remain at 45% auto and 42% manual for the next hour until preparations begin for retrofire.
04:26:33 Carpenter reports a problem with the ASCS system. He spends some six minutes trying to correct it and complete the checklist, finally reporting – I'm on fly-by-wire and manual.  
04:34:19 Responding to a query as to fuel reserves, replies – I have 20 and 5. 20 5
04:37:28 I'm out of manual fuel, Al.  
04:41:20 Fuel is 15 auto. I'm indicating 7 manual but it is empty and ineffective. 15 ?
04:43:22 We show you still have some manual fuel left. Cape.

Carpenter again repeats that he cannot get anything out of it.

04:45:14 I hope we have enough fuel.  
04:47:47 Still indicating 14 auto fuel. 14 ?
04:49:19 I think the ASCS has given up the ghost at this point. ? ?
04:50:20 Getting some pretty good oscillations now and we're out of fuel. 0 0

The retros worked as advertised. There was less kick felt by Carpenter because, as described previously, they fired off-line.


Posts: 124
Registered: Jul 2016

posted 12-07-2017 01:23 AM     Click Here to See the Profile for Jim_Voce   Click Here to Email Jim_Voce     Edit/Delete Message   Reply w/Quote
Spectacular response. Clarifies a lot. Thank you.

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