When Astra’s tiny Rocket 3.3 lifted off from its pad at Cape Canaveral Space Force Station on June 12, all seemed well. In fact, the mission was progressing exactly as planned until completion – the booster’s second-stage Aether engine appeared to be operating normally until it abruptly shut down about a minute before schedule. Unfortunately, the orbital mechanics are nothing if not demanding, and an engine burn that ends a minute earlier might as well never have happened.
According to telemetry values shown on screen during live coverage of the launch, the upper stage of the booster peaked at a speed of 6.573 kilometers per second, well below the 7.8 km/s needed to reach a stable low Earth orbit. While the video feed was cut as soon as it was clear something had gone wrong, the rigid physics of spaceflight means there’s little doubt about the sequence of events that followed. Without the energy to stay in orbit, the rocket’s upper stage would have been left in a sub-orbital trajectory, eventually re-entering the atmosphere and burning up a few thousand miles downstream from its starting point.
Of course, it’s no secret that spaceflight is difficult. Doubly for a startup that has only a few successful flights under its belt. No doubt Astra will determine why their engine quits early and make the necessary changes to ensure it doesn’t happen again, and if their history is any indication, they’ll likely be flying again shortly. Designed for a Defense Advanced Research Projects Agency (DARPA) competition which sought to spur the development of small, inexpensive rockets capable of launching payloads at short notice, the Astra family of rockets has already demonstrated exceptionally high operational agility.
Astra and the Rocket 3.3 design will live to fly again. But what about the payload the booster had to put into orbit? It’s a bit more complicated. It was the first of three flights planned to assemble a constellation of small CubeSats as part of NASA’s TROPICS mission. The space agency has already released a statement saying the mission can still achieve its science goals, albeit with reduced coverage, assuming the remaining satellites reach orbit safely. But if one of the next launches fails, both currently scheduled to fly on Astra’s rockets, it seems unlikely that the TROPICS program will be able to achieve its primary goal.
So what exactly is TROPICS, and why did NASA base its success on the ability of a small, relatively immature launch vehicle to perform multiple flights with its hardware on board? We’ll take a look.
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There is no shortage of Earth-orbiting weather satellites, but they operate largely isolated from each other. Partly because they’re all of different ages and technical abilities, but largely because they’ve always been designed as standalone missions. The TROPICS mission (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats) aims to fundamentally change this approach by using a constellation composed of identical CubeSats in low Earth orbit. These machines are equipped with high-resolution microwave radiometers. which can scan the satellite’s path above the ground, and with careful alignment of their orbital planes, should be able to provide scans of a given storm on a roughly hourly basis.
Compared to more traditional satellites, even the relatively modern NOAA-20 which was launched in 2017, this is a huge improvement. Operating independently, these satellites may only be able to image a storm every four to six hours, leaving critical gaps in coverage. The rapid scans made possible by the TROPICS constellation promise to greatly improve our ability to forecast and track deadly tropical cyclones, which have become increasingly frequent in the North and Middle Atlantic regions. According to NASA, this region has seen a record 30 named storms in 2020, and climate models expect things to only get worse from here.
TROPICS was designed to use six 3U CubeSats, each measuring 36 cm (14.2 inches) long and weighing only 5.34 kg (11.8 lbs). With the loss of the first two satellites on June 12, the constellation is down to four. The remaining satellites will still be able to image tropical storms and will no doubt provide useful data, but the reduced global coverage means the time between overflights will be increased. However, it should be noted that even at reduced capacity, TROPICS should still be able to deliver data faster than existing platforms.
Although it had a disappointing start, it should be remembered that TROPICS was ultimately a low-cost experimental mission. Even if the three launches had gone as planned, the mission was only supposed to last a year. As long as a single TROPICS CubeSat is able to reach orbit and use its equipment to scan an active tropical storm, the science goals of the mission will have been achieved, if not the most ambitious.
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Naturally, one wonders why a constellation of only six satellites has to be launched on three different rockets. After all, SpaceX launched up to 60 of its Starlink satellites per launch to create its own constellation. Couldn’t the six TROPICS CubeSats have been launched at the same time if NASA had reserved their passage on a more powerful rocket?
Technically, yes. But then they would not have been placed in the appropriate orbital planes to achieve the mission’s stated purpose of hourly flybys. Admittedly, this goal is probably already impossible to achieve due to the unexpected loss of the first pair of spacecraft, but if they had all been dropped along the same orbital path, their coverage would have been just as limited as the traditional weather satellites.
Couldn’t the satellites have maneuvered into their proper orbits once released, as Starlink satellites do? Perhaps if they were larger and had sufficiently powerful propulsion systems. But orbital plane shifts (i.e., changing the inclination at which a spacecraft orbits relative to the equator) consume an incredible amount of energy, especially in low Earth orbit, and tiny 3U CubeSats simply don’t have the capability to do maneuvers of this scale.
Given the specific mission objectives and the limitations of small, inexpensive satellites in flight, Astra’s rocket is actually the perfect vehicle to carry TROPICS. In fact, the needs of this mission aren’t that far removed from the original DARPA competition that Astra developed its booster for. The military wanted a rocket that could put small satellites into very specific orbits above the earth quickly and cheaply for reconnaissance purposes, it just so happens that those particular satellites are more concerned with force and motion tropical storms than troops and tanks.
That’s why, despite this disappointing setback, the next two batches of TROPIC satellites will almost certainly fly on Astra’s rockets, although they will now have to wait for the June 12 incident to be investigated. While other small boosters such as Rocket Lab’s Electron and even Virgin Orbit’s LauncherOne could potentially step in if absolutely necessary, the cost and expense of adapting the mission to a new launcher need not be underestimated. Besides, as the saying goes: Better late than never.
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