Hello, does anyone know why during the deorbitation maneuver the mercury capsule was positioned at approximately 34 degrees from the retrograde to ignite its retro pack?
The maneuver would not have been more effective in full retrograde?
Hello, does anyone know why during the deorbitation maneuver the mercury capsule was positioned at approximately 34 degrees from the retrograde to ignite its retro pack?
The maneuver would not have been more effective in full retrograde?
Not sure, but I can think of several reasons. One was that the very first thing the Mercury spacecraft did after separating from Atlas was to assume retrofire attitude. The nose-down attitude provided a view of the Earth for the astronaut, for one thing. The "tremendous" view was the first thing John Glenn talked about! One of several attitude indicators for the astronaut were markings on the window to align with the horizon, so perhaps that was the main reason. Another possibility was that those retrograde motors produced excess delta-v (Mercury had the option of a heavier heat shield at one point, if I'm remembering correctly), so they needed to fire off-axis a bit.
- Ed Kyle
The Delta T was fixed, and the time of retrofire was the only thing besides the attitude that could be controlled. Calculations were based on the -34 deg pitch. The attitudes held during retrofire determined the flight path trajectory during re-entry. You did not want to overshoot or undershoot the recovery area. Pitch was key for this. Yaw attitude determined the cross-range.
This gets to the heart of the matter of why they wanted a specific flight path coming back. Think in terms of the G-Loads and thermal loads on the heat sheild. Project Mercury is included.
Guidance and navigation for entry vehicles.
https://ntrs.nasa.gov/citations/19690010164
One of the things that just occurred to me is that the centerline axis of each of the three motors in the retro pack were at an angle to the centerline of of the spacecraft. I don't remember if they were fired sequentially, but if they were each motor could be aligned with the flight path by rolling the 120 degrees spacecraft before ignition of each motor.
The Delta T was fixed, and the time of retrofire was the only thing besides the attitude that could be controlled. Calculations were based on the -34 deg pitch. The attitudes held during retrofire determined the flight path trajectory during re-entry. You did not want to overshoot or undershoot the recovery area. Pitch was key for this. Yaw attitude determined the cross-range.
This is a 60 year old memory so I could be mis-remembering the events.
I seem to recollect that Carpenter [MA-7] was somewhat heavy handed on the fly by wire controls,
so he'd used up a significant percentage of the on-board fuel by the time of de-orbit after 3 orbits.
The de-orbit burn itself was done by the solid motors strapped to the heatshield so was the
same as other Mercury de-orbit burns.
So I suspect that there was insufficient fuel for maintaining the capsules attitude.
That could explain the overshoot of the primary landing area and the long time to recover.
Can anybody fill in the gaps?
thanks
Carl
The Delta T was fixed, and the time of retrofire was the only thing besides the attitude that could be controlled. Calculations were based on the -34 deg pitch. The attitudes held during retrofire determined the flight path trajectory during re-entry. You did not want to overshoot or undershoot the recovery area. Pitch was key for this. Yaw attitude determined the cross-range.
This is a 60 year old memory so I could be mis-remembering the events.
I seem to recollect that Carpenter [MA-7] was somewhat heavy handed on the fly by wire controls,
so he'd used up a significant percentage of the on-board fuel by the time of de-orbit after 3 orbits.
The de-orbit burn itself was done by the solid motors strapped to the heatshield so was the
same as other Mercury de-orbit burns.
So I suspect that there was insufficient fuel for maintaining the capsules attitude.
That could explain the overshoot of the primary landing area and the long time to recover.
Can anybody fill in the gaps?
thanks
Carl
Delay in the retro firing time and slow ignition
One of the things that just occurred to me is that the centerline axis of each of the three motors in the retro pack were at an angle to the centerline of of the spacecraft. I don't remember if they were fired sequentially, but if they were each motor could be aligned with the flight path by rolling the 120 degrees spacecraft before ignition of each motor.
no rolling was performed.
Was there a particular reason that the spacecraft hatch was offset to the side? It seems as if this was a particularly awkward arrangement that required the pilot to be a contortionist to enter the vehicle. It also wasn't really in keeping with the design philosophy of the American aerospace industry at the time, which emphasized entering the vehicle from above and directly into the seat. I can only think of the Bell X-1 and the Martin B-57A that had a similar side hatch arrangement.
If the hatch had been placed directly over the head of the pilot, it would have had to incorporate the window, but Gemini showed that this could be done without issue, and it would not have made a difference on the early spacecraft that had only portholes.
I am kind of scratching my head on this one. It must be something simple that I am missing.
Was there a particular reason that the spacecraft hatch was offset to the side? It seems as if this was a particularly awkward arrangement that required the pilot to be a contortionist to enter the vehicle. It also wasn't really in keeping with the design philosophy of the American aerospace industry at the time, which emphasized entering the vehicle from above and directly into the seat. I can only think of the Bell X-1 and the Martin B-57A that had a similar side hatch arrangement.
If the hatch had been placed directly over the head of the pilot, it would have had to incorporate the window, but Gemini showed that this could be done without issue, and it would not have made a difference on the early spacecraft that had only portholes.
I am kind of scratching my head on this one. It must be something simple that I am missing.
Access to the hatch opening mechanisms