When Astra’s little Rocket 3.3 lifted off its platform at the Cape Canaveral Space Force Station on June 12, everything seemed to be going well. In fact, the mission progressed exactly according to plan to the end – the Aether engine of the booster’s second stage appeared to be operating normally until it stopped abruptly, about a minute earlier than planned. Unfortunately, orbital mechanics are nothing but demanding, and an engine fire that ends a minute earlier might as well have never happened.
According to telemetry readings shown on the screen during the live coverage of the launch, the booster’s top stage reached a top speed of 6,573 kilometers per second, well below the 7.8 km/s needed to maintain a steady state. low Earth orbit. While the video feed was cut off 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 necessary to stay in orbit, the rocket’s upper stage would have been left in suborbital orbit, eventually penetrating the atmosphere and burning up a few thousand miles away from where it started.
It’s no secret, of course, that spaceflights are difficult. Doubly so for startups that have only a few successful flights to their name. There is no doubt that Astra will determine why their engine is shutting down early and make the necessary changes to ensure this doesn’t happen again, and if their history is any indication they will likely be flying again soon. Designed for a Defense Advanced Research Projects Agency (DARPA) competition seeking to drive the development of low-cost and small missiles capable of launching payloads at short notice, Astra’s missile family has already demonstrated unusually high operational agility.
Astra and the Rocket 3.3 design will live to fly again. But what about the payload that the booster would put into orbit? That’s a bit more complicated. This 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 should one of the subsequent launches fail, both of which are currently slated to fly on Astra’s missiles, it seems unlikely that the TROPICS program will achieve its primary goal.
So what exactly is TROPICS, and why has NASA based its success on the ability of a small and relatively immature launch vehicle to make multiple flights with their onboard hardware? Let’s see.
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There is no shortage of weather satellites in orbit, but they operate largely in isolation from each other. Partly because they are all of different ages and technical abilities, but mainly because they have always been designed as stand-alone missions. The Time-Resolved Observations of Precipitation and Storm Intensity with a Constellation of Smallsats (TROPICS) mission aims to fundamentally change that approach by using a constellation made up of identical CubeSats in low Earth orbit. These craft are equipped with high-resolution microwave radiometers that can scan the satellite’s track over the ground, and with careful alignment of their orbital planes, should be able to make scans of a given storm approximately every hour.
Compared to more traditional satellites, even the relatively modern NOAA-20 launched in 2017, this is a huge improvement. Working independently, these satellites may only be able to image a storm every four to six hours, leaving critical gaps in coverage. The rapid scans enabled by the TROPICS constellation promise to greatly improve our ability to predict and track deadly tropical cyclones, which are increasingly common in the Central and North Atlantic regions. According to NASA, this area saw a record 30 named storms in 2020, and climate models expect it to only get worse from here.
TROPICS is designed to use six 3U CubeSats, each 36 cm (14.2 in) long and only 5.34 kg (11.8 lb). With the loss of the first two satellites on June 12, the constellation has now been reduced to just four. The remaining satellites will still be able to image tropical storms and will no doubt provide useful data, but reduced global coverage will increase the time between flyovers. Although it should be noted that even at reduced capacity, TROPICS should still be able to deliver data faster than existing platforms.
While it was a disappointing start, it should be remembered that TROPICS is ultimately a cheap experimental mission. Even if all three launches had gone according to plan, the mission would only last a year. As long as even a single TROPICS CubeSat can reach Earth orbit and use its equipment to scan an active tropical storm, the mission’s scientific goals will have been accomplished — if not the ambitious ones.
Of course, one might wonder why a constellation of only six satellites needs to be launched on three different rockets. After all, SpaceX has raised a whopping 60 of their Starlink satellites per launch to build out their own constellation. Couldn’t all six TROPICS CubeSats have been put into orbit at the same time if NASA had booked their passage on a more powerful rocket?
Technically yes. But then they wouldn’t have been placed in the right runway planes to achieve the mission’s goal of flying over every hour. Admittedly, this goal is probably already out of reach due to the unexpected loss of the first pair of spacecraft, but had they all dropped off along the same orbit, their coverage would have been just as limited as traditional weather satellites.
Could the satellites not have maneuvered into their proper orbits after being dropped, as Starlink satellites do? Maybe if they were bigger and had powerful enough propulsion systems. But changes in the orbital plane (that is, changing the inclination at which a spacecraft orbits the equator) takes an incredible amount of energy, especially in low Earth orbit, and the tiny 3U CubeSats just don’t have the capability. to perform maneuvers of that scale.
Given the specific goals of the mission and the limitations of the small and inexpensive satellites being flown, Astra’s rocket is actually the perfect vehicle to carry TROPICS. In fact, the needs of this mission are not that far from the original DARPA competition for which Astra developed their booster. The military wanted a missile that could quickly and cheaply take small satellites into very specific orbits above the Earth for reconnaissance purposes, coincidentally, these particular satellites are more concerned with the power and movement of tropical storms than with troops and tanks.
That’s why, despite this disappointing setback, the next two batches of TROPIC satellites will almost certainly fly on Astra’s missiles, although they will now have to wait until after the June 12th incident investigation into the failure is completed. While other small boosters, like Rocket Lab’s Electron and even Virgin Orbit’s LauncherOne, could pop in if absolutely necessary, the cost and expense of adapting the mission to a new launch vehicle shouldn’t be underestimated. By the way, as the saying goes: better late than never†