Rocket Lab returns to flight following anomaly

by Sawyer Rosenstein

Rocket Lab launched its first Electron rocket since a failure on Sept. 19. The mission, named “The Moon God Awakens” launched on Dec. 15 at 7:00 pm NZDT (04:00 UTC).

The payload consisted of an Earth-observing satellite named Tsukuyomi-I for the Japan-based company the Institute for Q-shu Pioneers of Space, Inc. (iQPS).

The Anomaly

The Electron failure occurred during the mission named “We Will Never Desert You,” carrying the third satellite for the Earth-imaging constellation developed by Capella Space.

Rocket Lab CEO Peter Beck spoke with NSF during a recent NSF Live episode on YouTube about what happened during the flight. According to Beck, the first stage of the rocket flew exactly as planned, followed by a so-called “ignition transition” of the second stage.

“During that kind of ignition transient, there’s a whole bunch of stuff that obviously happens and… if you want to boil it down to its most elementary form possible, there was essentially an electrical arc occurred which pulled down the whole voltage,” Beck said.

The system aboard Electron consists of a high voltage and low voltage system. Beck commented that the arc from the high-voltage rail ended up downing the low-voltage rail as well.

“So we have that 500-volt rail there sitting at the potential,” Beck explained. “So when the arc occurred, if you go back to the live stream, you can actually visually see, you know, a big kind of greenish glow for a small amount of time. The whole of the whole event was about 1.6 seconds or so.”

Beck noted that the arc was as long as one meter.

The satellite for Capella Space encapsulated prior to launch. (Credit: Rocket Lab)

This is unique to this rocket because the upper-stage Rutherford Vacuum engine uses electric turbopumps to get propellant into the engine. The vehicle is currently the only orbital-class rocket in the world that uses such an upper-stage system.

Beck described Paschen curves, which in its simplest form is an equation resulting in a curve that determines at what voltage and what atmospheric pressure you are most likely to see an electrical arc.

“At a very partial vacuum in certain gases especially, it’s aggravated that you can form these big arcs,” Beck noted. “Now with Electron, of course, at stage separation, the rocket Gods wouldn’t be so kind to us. They put us in the worst part of the Paschen curve possible at that very point in time where the battery voltage is at its highest, of course, because there is a full battery.”

Beck noted that there was likely a very small leak allowing electrons to flow out and interact with the combination of trace amounts of nitrogen and helium, plus 500 volts of direct current with alternating current rippling on top of it in that unfortunate part of the curve.

Visible sparks at the point of anomaly during Rocket Lab’s launch. (Credit: Rocket Lab)

How they were able to determine all of this involved people who worked on movie sets.

Using the onboard cameras, they were able to recreate all of the lighting conditions and some unique shadows on the nozzle. Using those shadows, along with visible sparks, led them to this conclusion of an arc.

“The guy who did all the lighting work, we kept him segregated from the investigation team,” Beck said. “So he had no idea where the area that we were looking was. So it was a completely independent and isolated kind of project. And, you know, it was about a week or so in and we’d already identified this area as the most probable when he came in and presented as a results and it was, bang.”

Corrections to Electron

Beck noted that the best way to solve a problem is to delete the problem. After new instruments were used to test electrical potential fields down to microscopic levels, the team decided to pressurize the entire area near the batteries.

“[In] the upper stage, there’s a battery frame around the upper stage engine and we filled in all of the panels around the battery frame and put a flexible boot up to the nozzle,” Beck said. “So by pressurizing that area, it only needs to be like a half PSI, basically it’s like being down here on Earth. So there’s no way you can jump arcs at 900 millimeters or a meter. You basically remove any of that kind of Paschen law out of the equation.”

The rocket for this mission (left) and the rocket which experienced the anomaly (right). (Credit: Rocket Lab)

Beck noted they would be ready for the opening of this launch window in November as long as the customer was ready, which they are. He credits the team working hard hours to get to this mission. It is unclear why the launch got pushed from late November to the middle of December.

“The team has done an amazing job, like nobody slept for weeks and weeks and just plowed on through it,” Beck said. “It’s one thing to get to know the causes, it’s another thing to kind of implement pretty drastic corrective measures…in this timeframe and then go through all the testing and acceptance writing and whatnot.”

The Moon God Awakens Mission

Electron’s return to flight lifted off from Launch Complex 1B at its custom-built launch site in Mahia, New Zealand.

The payload is a synthetic aperture radar satellite that will collect high-resolution images of Earth. The satellite will join another iQPS satellite already in orbit. The goal is a network of 36 satellites that will be capable of monitoring the planet at specific fixed points every ten minutes.

A render of TSUKUYOMI-I in orbit. (Credit: iQPS)

While the official satellite designation is QPS-SAR-5, it’s also called TSUKUYOMI-I, named after the Japanese God of the Moon. That also influenced Rocket Lab’s naming convention for this mission. The satellite will launch into a 575-kilometer circular orbit inclined 42 degrees.

The satellite was originally set to launch aboard Virgin Orbit in 2022, however, the company went out of business before any iQPS satellites could be launched.

The Flight

Despite the changes to the upper stage following the anomaly, the carbon fiber composite rocket followed a timeline similar to previous missions.

At T-2 seconds, the nine Rutherford sea level engines ignite, running a mixture of Rocket Propellant 1 (RP-1), which is a refined form of kerosene, and liquid oxygen (LOX), followed two seconds later by liftoff. The 18-meter-tall vehicle will reach Max-Q, the point of maximum aerodynamic stress on the vehicle, at T+1 minute 4 seconds.

At T+2 minutes 40 seconds, the nine engines will shut down during an event known as main engine cutoff, or MECO. Three seconds later a pneumatic pusher separates the first and second stages. At T+2 minutes 46 seconds, the Rutherford Vacuum engine ignites. This is the portion of the flight where the previous anomaly occurred.

The fairings will separate about three and a half minutes into the flight. At T+6 minutes 43 seconds, the first of two engines powering the electric turbopumps is depleted. During a process known as hot swap, the first battery is jettisoned as the second battery takes over. The second stage will continue to run until T+9 minutes 32 seconds, at which point the second engine cuts off in a procedure known as SECO, followed by separation of a kick stage, positioned underneath the satellite, four seconds later.

TSUKUYOMI-I mated to its kick stage. (Credit: Rocket Lab)

The kick stage, powered by a 3D-printed Curie engine, ignites at T+54 minutes and 13 seconds into flight. This single burn will last 2 minutes 27 seconds, followed by the deployment of the satellite just one minute later.

(Lead image: Electron launches from the Mahia Peninsula in New Zealand. Credit: Rocket Lab)

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