Nov 28 2019

Progeny Mk6 Block I Flight 13 Analysis

Announced back in August, the Progeny Mk6 Block I was chosen to carry student-built experiments up into space two at a time. This will be the first time we are collaborating so directly with the various higher educational institutions around Kerbin and participation levels indicate the next generation of kerbs is eager to make their mark in space exploration! This mission was delayed from its original Nov 14th launch date due to the deadly attack on KSC last month, but all went well in the lead-up to launch with the rocket rolling out to the North Field launch site the day prior and tanked for a wet dress rehearsal. It was then left fueled for a condensed countdown on launch day. Structural panels are now attached underneath the launch base to prevent it from sinking off-kilter into the softer ground.

The Flight

The command to ignite the lower 0.625m solid rocket motor and begin the ascent was triggered by the AFCS and sent the rocket flying upwards at precisely 12:15:00.08 local time after an issue-less preflight. The rocket flew a standard ascent, dropping the first stage at L+35s and coasting to second stage ignition after the nose dropped 1.5° by L+40s. The second stage was detached cleanly to allow the 3rd stage to complete the burn up into space, reaching it just over 3 seconds after main engine cut-off at L+1m30s.

Although it still fell short of average height for Mk6-I rockets due to its mass, it made it noticeably higher than the previous flight with an apokee of 375.667km. The onboard experiments made good use of the extended time in space, filling the internal drives with science data. The rocket remained nominally oriented throughout the coast through space, slowly rotating relative to the planet so that its engine was pointing retrograde by the time it hit the top of the atmosphere at L+15m7s.

Although it did not travel as far downrange as the previous flight, it was still far enough to not regain signal once plasma blackout from re-entry heating took place, which cut the signal 7s after re-entry began and the rocket fell below the horizon another 6 seconds after that. This time the rocket came down only ~45km north of where the recovery vessel was holding station so it was able to reach the area in under two hours and found it still floating on the surface 315.383km downrange.

Flight Telemetry Data

Flight Analysis

Max Payload Capacity Nearly Exceeded

The only major issue with this flight was when the rocket re-entered and had to slow down to allow the parachutes to safely deploy. Because the rocket was about 30kg heavier than all previous Mk6 Block I flights it took longer for its speed to bleed off, even though it hadn’t flown as high as previous flights for the same reason. This plot below shows the difference 30kg makes:

Click for full size

So the 10th Mk6-I massed in at 1.721t versus this mission’s 1.745t and even though it flew up to 517km and thus came down traveling faster it was able to slow down quicker once it hit the denser atmosphere and deployed its air brakes.

A full check of the air brakes and recovered parachute were conducted upon the return of the rocket and were found to be working properly so they did not contribute to the slow deceleration.

This is an important reminder to mission planners that it’s not just about how much mass a parachute can lower. The payload still splashed down at rates similar to lighter loads once the chute was fully deployed. Taking into account the extra energy that comes with extra mass while the vehicle is in motion and thus requiring more stopping room was not an issue that was fully considered and almost cost us the payload on this mission, as the chute did not fully arrest the descent until just 58m!

Future Plans

The final two upcoming launches in December have already been load balanced and thankfully will mass slightly less than the first 4 experiments so there’s no danger of exceeding recovery limits. With no major changes needed to the rockets the assembly schedule should remain on track and Lead Engineer Simon says he’ll be able to task VAB workers back on Ascension duties sooner rather than later as well.