Hailing a taxi for your satellite: Interview with Momentus. Part I

Visiting Momentus factory in Silicon Valley

In early June our partners, California-based startup Momentus, invited Precious Payload team to their factory. Momentus is a developing in-space shuttle service, using safe water-plasma propulsion technology, for taking satellites from where the rockets drop them off to a custom orbit. Negar Feher, VP of Product and Business Development of Momentus, has taken us on a tour, has introduced the team, and has given us a big #knowyouroptions interview.

 

Propulsion Team

Negar Feher: There is our propulsion team. We’re not gonna bother them, ‘cause they’re very busy. Mark Crawford, our aerospace engineer, is modeling our thrusters and working on drawings related to that and improving it, and he has an awesome background in this. He was part of the team that manufactured El Camino Real our first mission in less than six months from contract to launch. I’ll show you more when we go in a hallway. It’s an incredibly dedicated amazing team that just makes the impossible happen. 

AM: Very good. So this is like the design bureau here?

NF: Yes. So, this is the propulsion design group and I’ll take you to the other side of the building where our spacecraft is… Over here is the replica of El Camino Real. It’s the first mission that I was mentioning to you that we’ll get flying in July. What you see here is our propulsion system.

AM: It’s that small!

NF: It looks like the size of a hockey puck. And that little circle you see there is where the thrust comes out and then we have the vaporizer, it goes in there. And this is just the structure that holds it, this props, you can see it here, inside this is the 16U demo that we’re doing. That’s what you see there is right there. The prop tank and the entire feed system. And this is an image of what the plume looks like coming out of it.

And the intent of this mission this year is to basically show that this type of water plasma propulsion system works in space, that we get data from space on how much thrust it generates, what the efficiencies are, etc to compare that to the data that we’ve gathered here.

AM: Basically to verify the data that you came up with in your lab.

NF: Exactly. So it’s like a verification test. And it flies a lot of the avionics and electronics that we’re gonna be flying on our next Vigoride mission next year.  So this is the first mission we’re flying.

AM: I think this is also the first that big of a CubeSat that has been launched ever.

NF: This is the first 16U CubeSat ever been launched…

AM: You’re pushing the limits of the standard.

NF: We built it with AstroDigital on this one. They built a lot of the spacecraft structure and avionics and electronics, and they’re also one of our vendors for Vigoride and others. They’ve been a great partner. And, you know, we worked with them for building and launching the satellite in like less than six months, which was an amazing team. So you will hear more about that launch. It’s gonna be the launch of the Soyuz in Vostochny on July 5.

AM: Keeping our fingers crossed.

Propulsion Laboratory

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NF: This is our prop lab. This is Charlie Feng, our aerospace engineer.

AM: Hey, Charlie, nice to meet you.

CF: Nice to meet you… So we’re doing some thruster testing currently. We have a small Vigor thruster. This is the chamber that we’re testing, the thrust stand is built-in. We have external testing as well. Currently, we’re doing some bench testing to build some new prototypes that are going to point where we have good confidence in them. Put them chamber, see how the changes affect the thrust, see what changes are beneficial and eventually, we’re trying to take it to our endurance chamber, so there’s got to be up to three thrusters in here all firing simultaneously.

AM: Inside that chamber, right?

CF: That gets us some better idea of the left time of these thrusters. This is the amount of testing we’re conducting here. 3,000 hours for one of the tests.

AM: 3,000 hours! Continuous?

CF: Not completely continuous. They are being cycled. We have pretty high confidence that these thrusters will do their job for the mission here.

AM: Amazing.

NF: And yeah, so, basically, the mission is showing the El Camino Real will get the results from that will be compared against some of the results that he gets under vacuum here to kind of check, kind of like a calibration check

AM: Yeah, and it feels like you can also test the bigger versions of your Vigoride here, right? Probably, the Vigoride Extended as well?

NF: Right. So what we’re gonna test in here is just the propulsion system. We’re not gonna test the entire Vigoride in this chamber. Probably, it’s not gonna fit.

AM: Ok, the actual propulsion module…?

NF: This is the sub-system level test setup. When we get to the big level system test where we have the entire Vigoride or Vigoride Extended, we have here. And you can see these big boxes here. These are what we’re setting up now for larger vacuum chambers that will do system-level environmental testing. So what the environmental testing will do is basically dictated by the launch vehicle in addition to our requirements. We have to test it in the vacuum, we have to put it under vibration, sound vibe …by acoustic testing, etc. So, these all will be done at the next high level. So, these are sub-system level here. And this is a really awesome chamber that Charlie has set up for us. It has differential ion pumps, which allows getting down to like 10^{−11  torr}.

Spacecraft Team

NF: In terms of our team, the spacecraft team is over there. There are Aaron Mitchell and Sam Avery, our systems engineers. They’re working on developing Vigoride. We have our PDR, for example, tomorrow or the day after tomorrow, so they’re very busy right now.

Integration and Test Laboratory

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NF: Right now you see high power thrusters set up in here and a little vacuum chamber. These are called vacuum cubes, where we put thrusters to test them. The thrusters aren’t here right now, so I can’t show you them, but we run the setup here.

Eventually, when we’re done with this, early next year, construction in this building will have been done, and this is where we will be assembling our Vigoride and integrating the customer payloads onto Vigoride and doing testing on them here.

AM: And from here you will ship the integrated Vigoride with all the customers’ satellites to the launch facility?

NF: Correct. And because we use water, we can fuel it here.  So we will fuel the whole orbit transfer vehicle, Vigoride, here, and then we’ll integrate all the satellites. And then we’ll package it all up and we’ll ship it to launch phase. And it’s so safe that even with our first vehicle, El Camino Real, we’ll be able to ship in like a passenger aircraft. We’ll just book an economy seat, put a satellite fueled into the chair and just ship it, fly it with an engineer.

AM: Really? A fueled…?

NF: Yes, It’s so amazing. And the biggest problem that they had was actually the TSA wanting to go through the security and the fact that it had more than two-three milliliters of water? they had to swab it. But that’s the way we’re sending it off there. So yeah, that’s kind of CONOPS.

In terms of testing, we’ll probably have each of the satellites do the testing at the satellite level. So, they’ll do their own TVAC, etc to comply with launch vehicle requirements.

AM: At their facility?

NF: Right. And then we’ll integrate it all together here and then we’ll ship it.

AM: And then what operations will, if any, remain at the launch facility?

Nf: We don’t need them to do anything for us at the launch facility since we fuel here. Usually, the operations that are done at the launch facility involve a lot of fueling and hazardous operations. We have no hazardous operations, so we’ll be doing everything here. There we might need to charge a battery or something like that. Imagine just plugging it in – that’s all that we need to do.

AM: So there’s no need for the late access to your satellites at the very last moment before the launch to refuel it?

NF: No.

AM: It’s amazing.

NF: No. That’s what’s making it so cost-effective. So it’s very exciting. You can see this is an office building and we can build everything here because we’re not using any hazardous material. We can use regular plumbing material, ‘cause it’s just water. Like plastic tubing.

AM: Think to plumb in space, 2019. 

NF: We’re space plumbers.

Interview with Aaron Mitchell, a systems engineer of Momentus

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Andrey Maksimov: Can you explain, what do you do at Momentus? What’s your role at Momentus?

Aaron Mitchell: So, my role is a space system engineer, but, as we need a lot of hands here, I also do a lot of astrodynamics and mission design as well, so I help make sure all parts of the spacecraft are designed properly and interact with each other properly, and then I also do the design of the orbital trajectories that we use to take our customers from one place to another in space.

AM: Can you tell us a few words about how this technology works, the propulsion technology?

AaM: Yeah, so the microwave electrothermal thruster or MET is actually a very simple device, which gives it a lot of its advantages. It’s basically very similar to heating up water in a microwave. And that, combined with the fact that we use water itself, means that the device is very robust, but still capable of high performance both in terms of efficiency and thrust, which is really what I think the future of space economy needs. It’s some kind of balance between the two of those.

AM: The way we initially explained it to our customers is it’s like a kettle that you put into a microwave.

AaM: Yes, yes!

AM: [Is this] the right assumption?

AaM: Yes, that’s very accurate, actually. You know, when steam comes out of that part of the kettle that makes the whistle, that’s basically like our nozzle.

AM: So, the kettle in the microwave, right?

AaM: Yes, yes.

AM: And what kind of temperatures can you achieve in that environment?

AaM: You know, temperatures are a tricky thing because there’s average temperature, there’s point-instantaneous temperature. The amazing thing about what our device can do is it can achieve very high-temperature gradients, so we can have very very hot things next to very very cold things, and that’s really good because your performance is limited by how hot you can get something. But at the same time, your lifetime is limited by how hot are the things, how hot are the parts of your rocket exposed to.

AM: Right, how the part actually withstands this heat…

AaM: Exactly, yeah. So, we’re able to get very very high temperatures along the axis of our thruster, we’re talking thousands of Kelvin, while simultaneously we are having hundreds of degrees in C outside of the chamber near the walls where you can start melting things. So that allows us to have very long-life, robust thrusters that are not complex design or… Sorry, they are tricky to design but are not complex to manufacture at all.