How do you know that the calculations were wrong? Did you check the math? Do you even know what math would be involved?
Yes, I checked everything
Shows us your calculations where you checked everything.
I asked Glenn and he referred me to this NASA assistant of his that checked everything incl. fuel back in 1962 - Katherine Johnson. She died Feb. 24, 2020 at the age of 102!
For Glenn to finish his space trip (to land on Earth again) he had to brake hard three times by firing his rocket engine in the opposite direction of travel and Katherine checked it all!
Why do you totally misrepresent what really happened? Are you just ignorant or trying to be deceptive?
Sure, John Glenn did ask Katherine Johnson to double check the computer calculations:
Katherine Johnson, Hidden Figures, and John Glenn’s Flight
Right at this time, the center installed the first large IBM mainframe computer, foreshadowing an age when the job title would go away and the women would adapt to becoming computer scientists. In fall 1961, as the Mercury project prepared for Glenn’s launch on the Atlas intercontinental ballistic missile, Glenn asked one of the supervisors to have “the girl,” meaning Johnson, to check the reentry calculations of the new computer on the old desktop calculators—he just was not comfortable with having his fate dependent on a machine. Johnson did that extensive work, which took a couple of weeks, and became known for it in the African American press after the flight.
Sure, John Glenn did fire three
little retrorockets to start his reentry
but look at this:
The Voyages of John Glenn
He’d lined up the capsule to the proper attitude, with the retrorockets aimed 34 degrees above the horizontal, pointing into his flight path. With half a minute to go, the capsule’s auto-sequencer began its own countdown for retrofire. Friendship 7 was crossing the coast of California when Schirra read the final seconds: “Five, four, three, two, one, fire.”
Glenn felt a solid push as the first of three solid-fuel retrorockets began firing. His mission clock showed that since liftoff, 4 hours, 33 minutes, and 7 seconds had elapsed. Seconds later, he felt the second one go off, then the third. He felt as if he were suddenly flying back toward Hawaii, but it was just an illusion caused by the sudden acceleration after almost four and a half hours of weightlessness. In reality, the retros had only slowed Friendship 7 by about 340 mph, enough to cause it to fall out of orbit.
So "three solid-fuel retrorockets began firing . . . . only slowed Friendship 7 by about
340 mph".
This makes your "he had to
brake hard three times by firing his rocket engine in the opposite direction of travel" totally misleading
The automotive sequencer fired "
three solid-fuel retrorockets began firing" (not his "rocket engine").
There was no "brake
hard three times" - those three solid retrorockets only reduced the velocity "about
340 mph"!
The slowing down from about (17,000 – 340) miles per hour to sub-sonic velocities had to be by
atmospheric braking and that was a bit "hairy" for John Glenn.
The rest is tl;dr and is just for interest.
The Voyages of John Glenn
What Glenn did not know, as Friendship 7 drifted over the night side of Earth for a second time, was that mission controllers in Cape Canaveral were aware of a serious and potentially deadly problem with his spacecraft. It had to do with the landing bag, a tube of rubberized fabric that was folded, accordion-style, between the heat shield and the craft’s base.
Normally the landing bag would be deployed just before splashdown in the ocean; the weight of the heat shield would cause it to expand and inflate with air, cushioning impact with the water. But one of the many telemetry readings streaming down from Friendship 7 indicated that the bag had already deployed.
It was probably a faulty signal—but what if it wasn’t? In that case, the only thing holding the heat shield on would be the retrorocket package, which was secured by three straps attached to the capsule’s base. Once the retrorockets fired to slow Friendship 7 out of orbit, the retropack would be jettisoned, the heat shield would come loose, and when temperatures outside the capsule rose to 9,500 degrees during reentry, there would be nothing to protect John Glenn from incineration.
It seemed the only solution was to leave the retropack attached during reentry; its straps would burn away, but by that time aerodynamic forces would hold the heat shield in place. But while it was still attached, would it make the capsule unstable? And as it melted away, would it cause fatal damage to the heat shield? The anguish of uncertainty hung over Flight Director Chris Kraft and his team. They would have to come up with an answer before retro-fire time, which was less than two hours away. For now, Kraft decided, they wouldn’t say anything to Glenn. There was no point in worrying him with a problem he couldn’t do anything about.
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John, leave your retropack on through Texas. Do you read?” It was Wally Schirra, from the ground station in Point Arguello, California. Glenn knew that in Mercury Control, people were deliberating about the landing, but right now there wasn’t time to dwell on that; retrofire was less than a minute away.
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As Glenn flew within range of Cape Canaveral for the final time, Shepard finally told him what was going on: “We are not sure whether or not your landing bag has deployed. We feel it is possible to reenter with the retropackage on. We see no difficulty at this time in that type of reentry.”
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