Interview #3

Student Name: Ismail Hozain

Name of person interviewed: Wyatt Rehder

Profession: Rocket Telemetry Technician

Location and business name: Alaska Aerospace, remote

Date of interview:11/10/21

Time: 1pm

During the interview we began by talking about what he did at hig job which was to operate and maintain the radio antenna and telemetry systems for Alaska Aerospace’s Kodiak launch site. He described it as getting black boxes and making them speak to each other. He also at one point in time worked for Masten Space Systems on an internship but said that as cool as their stuff was, they didn’t pay very much. He oversees and does mission control for 1-6 launches a year for mid-sized launchers like Astra and Rocketlab. SpaceX, ULA and Ariane do their own telemetry and launch control. It is much easier to vertically integrate all of that but smaller companies are not able to do it because they have much bigger fish to fry.

He used to be a commercial fisherman, got an engineering degree and then got into the electrical engineering side of things and soon enough found himself working on rocket telemetry. He works on building small liquid rocket engines in his free time which gives him plenty of experience on the test stand in addition to his time at MSS. We then pivoted to speaking about the test stand protocols such as vent locations, hydrostatic test procedure and DAQ systems. He agreed with Ken’s solution of not using a load cell and just measuring chamber pressure, and mass flow rate to calculate thrust. One interesting fact is that a lot of telemetry can be gained just by pointing a camera and microphone at the engine giving the engineers insight into combustion instability and resonance frequencies as well as flame temperatures and exhaust velocities. Once you have a few of these items it becomes very very easy (take this with a grain of salt, it’s rocket science after all) to calculate and plot the rest of your items.

I had been planning on using 2 arduinos as my DAQ system since I have them lying around and can easily get some thermocouples and universal breakout boards and some cheap chinese pressure transducers to get the necessary engine telemetry. He said that he would use a Teensy for far more processing power but agreed with my decision to just use what I had lying around. At this point he agrees with me and Ken’s decision to just push for a static fire as soon as possible and skip out on relative quality of life improvements and superior setups in lieu of just making it work. In this case faster, cheaper and inferior solutions > more time and resource intensive ‘better’ solutions. The arduino is one of those decisions. I also chose a very low sampling rate for my transducers so I can just go with cheaper ducers. They don’t even mention a sampling rate so I assumed a worst case scenario of either 10-100hz. Either is fine for my application.

One thing we spoke about is getting an oil-free air compressor, a line filter and some IPA to LOx clean everything that sees liquid oxygen. Things that come in contact with LOx have to be very clean, any hydrocarbons will either vaporize or explode depending on the mass of the FOD (Foreign object/ debri). I should be okay but he said to still have a local mentor help me with the process. He asked me about the vent locations and when I did not have an answer he said that I should make sure I have a vent line for the lox tank and make sure that it vents away from the fuel line so they do not combust and make sure the vents are not anywhere near things I will be touching just so I don’t burn myself when the engine is done firing. Said that pretty much the only thing that can neuter a test stand is a fire and to try really hard to not set the stand on fire as it will consume all the wiring and expensive telemetry.

I’ll be using these tips to improve my chances of getting a usable engine + test stand and not a pile of ashes. :)

Ismail