When the Astra small rocket 3.3 rose from its pad at the Cape Canaveral Space Force Station on June 12, everything seemed to be going well. In fact, the mission was just beginning to plan for the end – the booster’s second-stage ether engine seemed to be working normally until it suddenly shut down about a minute before the scheduled time. Unfortunately, orbital mechanics is nothing if not accurate, and an engine burn that ends a minute earlier may never have happened.
According to the telemetry values shown on-screen during the launch’s live coverage, the top layer of the booster peaked at a speed of 6.573 kilometers per second, much less than the 7.8 km / second required to reach a stable low Earth orbit. Although the video feed was cut as soon as it became clear that something was wrong, the inflexible physics of space flight meant there were very few questions about the sequence of events that followed. Without the necessary energy to stay in orbit, the upper layer of the rocket would be left in a sub-orbital trajectory, eventually re-entering the atmosphere and igniting thousands of kilometers below where it started.
Of course, it’s no secret that spacecraft are tough. Double up for startups so they have a few successful flights under their belts. There is no doubt that Astra will determine why they will shut down their engines early and make the necessary changes to ensure it does not happen again, and if there is any indication of their history, they can fly again in a short order. Designed for a Defense Advanced Research Projects Agency (DARPA) competition aimed at encouraging the development of cheap and small rockets capable of launching payloads at short notice, the Astra Rocket family has already shown unusually high operational agility.
The Astra, and Rocket 3.3 design, will survive to fly again. But what was the reason for putting the payload booster in orbit? It’s a little more complicated. It was the first of three flights planned to assemble a constellation of small cubesets as part of NASA’s Tropics mission. The space agency has already issued a statement saying the mission could still achieve its scientific goal, albeit with low coverage, assuming the remaining satellites have reached safe orbit. But if one of the subsequent launches fails, both of which are currently scheduled to fly on the Astra rocket, the Tropics program does not appear to be able to achieve its initial goal.
So what exactly is Tropics, and why has NASA pinned its success on the ability of a small and relatively immature launch vehicle to make multiple flights with their hardware onboard? Let’s see.
Getting closer to action
There is no shortage of weather satellites in Earth’s orbit, but they operate in isolation from each other. Partly because they are of different ages and technical abilities, but mainly because they were always designed as a single mission. The goal of time-solving observations of precipitation structure and storm intensity with the TROPICS mission is to radically change that pattern using a constellation made up of identical cubesat in low Earth orbit. Which can scan across satellite tracks across the ground and carefully align their orbital planes, should be able to provide a given storm scan on an hourly basis.
Compared to the more traditional satellite, even the relatively modern NOAA-20 that was launched in 2017, this is a huge improvement. Working independently, these satellites may be able to capture only one storm every four to six hours, leaving a serious gap in coverage. Rapid scans made possible by tropics constellations promise to greatly improve our ability to predict and track severe tropical cyclones, which have become increasingly common in the Central and North Atlantic regions. According to NASA, the region saw record-breaking 30 so-called hurricanes in 2020, and climate models are expected to get worse.
The Tropics were designed to use six 3U cubes, each 36 cm (14.2 inches) long and weighing just 5.34 kg (11.8 lb). With the loss of the first two satellites on June 12, the constellation has now dropped to just four The remaining satellites will still be able to take pictures of tropical storms and will undoubtedly provide useful data, but the reduction in global coverage will mean an increase in time between flyovers. Although it should be noted that even in reduced capacity, TRPICS should still be able to deliver data faster than existing platforms.
When making a disappointing start, it should be remembered that TROPICS is ultimately a low cost experimental mission. Even though all three launches went as planned, the mission was only supposed to last one year. As long as a single tropics cubsat is able to reach orbit and use its equipment to scan an active tropical storm, the scientific goals of the mission will be met – if not ambitious.
Naturally, one would wonder why a constellation of only six satellites needs to be launched on three different rockets. After all, SpaceX is loafing more than 60 of their Starlink satellites per launch to create their own constellations. If NASA had booked their passage on a more powerful rocket, wouldn’t six of the Tropics cubesat have been launched into orbit at the same time?
Technically, yes. But then, they were not placed in suitable orbits to achieve the stated goal of the overflight mission per hour. Admittedly, these targets are probably already unattainable due to the unexpected damage to the first pair of spacecraft, but if they were deposited along the same orbital track, their coverage would be as limited as those of conventional weather satellites.
Couldn’t satellites like the Starlink Satellite have gone into their proper orbit? Probably if they were bigger, and had a strong enough propulsion system. But changes in orbital planes (i.e., changing the tendency of a spacecraft to orbit the equatorial reference) take incredible amounts of energy, especially in low-Earth orbit, and tiny 3U cubesats simply do not have the ability to make tactics. That’s the scale.
Given the mission’s specific goals and the limitations of small and inexpensive satellites, the Astra rocket is actually the perfect vehicle to carry tropics. Indeed, the requirements of this mission have not been so far removed from the original DARPA competition that Astra has created their booster. The military wanted a rocket that could quickly and cheaply land small satellites in very specific orbits on Earth, just because these specific satellites are more concerned with the power and movement of tropical storms than with troops and tanks.
Because of this, despite this disappointing push, the next two batches of TROPIC satellites will almost certainly fly into Astra’s rocket, although they will now have to wait until the June 12 failure investigation is complete. While other smaller boosters, such as Rocket Lab Electron and even Virgin Orbit launchers, could potentially stand if absolutely necessary, the cost and expense of adapting the mission to the new launch vehicle should not be underestimated. In addition, the proverb goes: Good late.