On September 24, the capsule of the OSIRIS-REx mission successfully landed in the Utah desert. His parachute seemed to have had a little delay in opening, although this was not a problem. In reality, an internal investigation has just shown that NASA came close to disaster.
These are exceptional samples. Small pieces of asteroids (several tens of grams all the same) which are studied in laboratories and are just beginning to reveal their secrets. The OSIRIS-REx mission, which took off in 2016, was to collect them from the surface of the asteroid Bennu, and to “deposit” the capsule containing its precious pieces on Earth on September 24. NASA teams, live and in coordination many times repeated, spotted the capsule under its parachute which apparently had a little head start, then recovered it from the ground before transporting it with every possible precaution towards their laboratory in Houston, Texas.
Yes, but surprising all the same, this advance on schedule, no? The engineering team in charge of the project studied the images of this return, the telemetry data and the radar readings… And their conclusion is very simple, NASA was really lucky. Because the parachute system was simply poorly wired.
A slight connection problem
However, the system is only made up of three wires, each of which controls a particular sequence of deployment on this small capsule! The first is intended for the small control parachute, the “ drug drop “. The latter, which is normally ejected around 35km altitude, does not significantly slow down the capsule, but it allows it to orient itself correctly (shield downwards) and stabilize its flight. The second and third wires are used a few fractions of a second apart: we cut the main attachment point (action no. 2) of the chute, and we immediately order the ejection of the main parachute (action n°3), which is driven by the attachment cable, when the system is at approximately 3 km altitude. In short, three sons. Not very complicated, in theory.
But, and this is where it gets complicated, once the system is delivered to be packaged in the flight capsule and plugged in, there is no longer any question of testing it, obviously (otherwise you have to put back the pyrotechnic system, fold the parachutes , and redo everything). To top it off, no one noticed, but two connections were reversed, because a label indicated “main” and designated two different actions on the control system and on the control system. parachutes.
A little luck and a strong parachute
As a result, what happened? Arriving at an altitude of 35 km, the on-board system of the capsule containing the precious samples sent its signal to the poorly wired system: the drug chute did not deploy, because in reality the system had just shut down the attachment point of the drug falls… which was still folded into its case. And he stayed in it for another 30 kilometers of fall! So, it is not surprising that the capsule arrived at the ground early, it was slowed a little less than expected, and fortunately its aerodynamic shape made it possible to maintain its stability during the descent.
At an altitude of 3 km, the on-board system controls the other actions, and this time the chute and the main parachute are ejected almost at the same time. The drug drops fly away, absolutely useless. Here again, luckily, the main parachute opens alone (normally it is helped by the falling drug…), does not get tangled on itself, does not destabilize and slows down the capsule sufficiently so that finally, at a few hundred meters from the ground, everything finally returned to normal. The OSIRIS-REx samples land in the desert with all the required gentleness.
It didn’t seem like anything. But it didn’t go far…
Source : NASA Blog
9