Astra: Fight again and again despite repeated failures, so what if the rocket flies

On August 29, 2021, Astra's "Rocket 3.3" was launched at the Pacific Spaceport in Alaska. After ignition, one of the five engines of the first-stage rocket worked abnormally, resulting in unbalanced thrust. The rocket first moved sideways on the launch pad, then barely flew upwards, but because of a serious attitude error, the launch controller had to interrupt the flight, and the rocket eventually fell into the Pacific Ocean.

Astra, which is currently working to develop a small rapid-response rocket for the U.S. Defense Advanced Research Projects Agency, is perhaps the most typical example of small rocket companies struggling between cost and performance.

Astra is mainly planning to provide the military with a small rapid response rocket to launch satellites in case of emergency according to battlefield needs. Its launch capacity can send a payload of about 150 kg to a low-Earth orbit of 500 kilometers. Astra was established in October 2016 and put its first rocket on the launch pad in March 2018, which sounds pretty fast.

The company was very lazy when naming its rockets, and just called them "Rockets". The first model was called "Rocket One". However, this "Rocket One" could not launch satellites into orbit, but was only used to test the first-stage rocket engine "Delphin", which means "Dolphin" in German. The second-stage engine was called "Ether", which had not been developed at the time, so it was just a counterweight.

In July 2018, Rocket One was launched. However, it is reported that between March and July, Astra tried to launch rockets many times but failed. The launch on July 20 was also unsuccessful. Rocket One was launched from the Alaska launch site, but it flew for only 27 seconds before an abnormality occurred and fell back to the ground. The landing point did not exceed the fence of the launch site. However, the president of Astra told reporters that the customer was very satisfied with the result of this launch.

Four months later, Astra launched another rocket, which flew for 30 seconds before aborting and falling to the ground. The company claimed that the launch was a success.

The launches of Astra's 1.0 and 2.0 rockets should be considered successful, because they only have one stage and are only sent vertically into the sky, not into orbit, so the difficulty is not too great. However, during the 3.0 period, Astra must develop a launch vehicle that can enter orbit, so the difficulty of the problem immediately increases exponentially.

Can't get on track anyway

The third version of the rocket is the model that will actually enter orbit, and its numbering is in the form of 3.x. The first one is called "Rocket 3.0". This rocket is used to officially carry out the launch mission of the US Defense Advanced Research Projects Agency. Originally, March 2, 2020 was the last launch window for Rocket 3.0, but because the ground preparations were not completed, this window was missed. However, the US Defense Advanced Research Projects Agency did not withdraw its support for Astra, and they asked the company to continue to carry out the launch mission.

On March 23, Rocket 3.0 was finally ready to launch again, but it caught fire during launch preparations. At that time, ground technicians completed a drill, but for unknown reasons, the rocket caught fire and completely burned the entire rocket. It is said that there was no satellite on the rocket at the time, so there was no loss of payload.

After the destruction of Rocket 3.0, Astra continued to challenge the first cosmic speed. On August 31, 2020, Rocket 3.1 was erected on the launch pad, but the weather was not good and the launch had to be postponed. On September 12, Rocket 3.1 finally ignited, but soon fell back to the ground and exploded in an empty field. Astra officials said that there was no payload on this flight, so the loss caused by the failure was not great.

The next rocket is 3.2. On December 15, 2020, Rocket 3.2 took off from Alaska. This time it seemed to be close to success. The rocket successfully crossed the Karman line and reached an altitude of 390 kilometers. This was originally the orbit where it was supposed to deploy satellites, but due to problems with the fuel mixing of the upper stage engine, the simulated payload did not reach the first cosmic speed. But Astra announced that the mission was a success, because their experimental goal was to achieve the first stage shutdown and the first and second stage separation. As long as this can be done, it will be considered a mission success, so people will just listen to it.

Rocket 3.3 Flying Sideways On August 29, 2021, Rocket 3.3 was launched at the Pacific Spaceport in Alaska, but failed again. The failure was described at the beginning of this article. Kemp, the company's co-founder and CEO, said in a telephone press conference about 90 minutes after the failure that one of the five engines of the first-stage rocket failed less than 1 second after takeoff for unknown reasons, resulting in the launch failure.

You may ask, if a rocket engine fails, won't the rocket explode? Why is Astra's rocket so "tenacious" that it struggled for a while and still flew up? This has to start with the flight principle of the rocket.

We know that in order for a rocket to achieve the speed of upward flight, the thrust of its rocket engine must be greater than the weight of the rocket. For this indicator, there is a special term in the industry, called "thrust-to-weight ratio". According to the information released by Astra, the rocket launched this time uses liquid oxygen and kerosene propellants, is 11.6 meters long and 1.32 meters in diameter, and is designed to fit into a standard freight container. The designed sun-synchronous orbit carrying capacity is 25 kilograms and the low-orbit carrying capacity is 100 kilograms. The first stage of the rocket is equipped with 5 "Dolphin" engines driven by electric pumps, with a total thrust of about 140 kilonewtons; the second stage is equipped with a single "Ether" engine, with a vacuum thrust of about 3.1 kilonewtons.

During this launch, the rocket was able to stay above the ground and move sideways close to the ground even though one of its engines failed to work, indicating that the thrust generated by the remaining four engines that were still working was exactly equal to the weight of the rocket. At this point, the rocket could not gain the acceleration to fly upward. However, as the rocket engine continued to consume propellant, the total mass of the rocket continued to decrease. When the propellant was consumed to a certain extent, the rocket gained the acceleration to fly upward again and began to climb again.

You may have another question, that is, why did the rocket not float in place, but instead shifted sideways?

This means that the engine that failed in the rocket was not placed in the middle of the five engines, but on one side. In this case, the thrust of the rocket is unbalanced, and theoretically the rocket should fall to the ground, but why didn't it fall to the ground? This is thanks to the rocket's attitude control system.

We know that general launch vehicles have guidance systems and control systems. The guidance system is responsible for telling the rocket when to turn, how much to turn, and under what conditions to shut down the rocket engine. Following the instructions of the guidance system, the launch vehicle will eventually reach the predetermined orbit.

So who directs the engine deflection and controls the rocket to execute the instructions of the guidance system? It is the rocket's attitude control system.

The attitude control system must sense the current attitude of the rocket at any time and adjust the deflection direction of the engine to return the attitude of the rocket to the position specified by the guidance system. During this period, the attitude of the rocket will inevitably be subject to various disturbances, and the attitude control system must overcome these disturbances and control the attitude of the rocket.

When a rocket is launched, the guidance system usually gives the command to fly vertically 90 degrees upward. When an engine installed on one side of the Astra rocket failed and shut down, the rocket's center of gravity was much higher than the position where the engine thrust acted. In order to maintain the balance of the rocket, the rocket attitude control system had to control the engine to swing to the other side to generate the opposite thrust torque, so that the rocket's attitude could be kept in a vertical state as much as possible. However, this would also produce another side effect, that is, the rocket gained a lateral force, pushing the rocket to fly sideways.

Telemetry data showed that the rocket had reached an altitude of about 50 kilometers above the Earth's surface when ground control personnel shut down the engine. So Astra is still a long way from a successful launch.

Although the launch failed again, it does not seem to have affected Astra's ambition to win. According to them, although the past three orbital flights have failed, each one is closer to the ultimate goal of success, that is, entering low-Earth orbit.

The company's head cheered himself up on Twitter, saying that he was extremely proud of the team and that conquering space might be difficult, but just like this rocket, we will not give up. Such bold words sound very touching, but in fact, what really made him not give up was the approximately $100 million investment he had already received. With such a large sum of money as a backing, plus the pre-sale contract from the US Defense Advanced Research Projects Agency, the company can certainly continue to advance its trial and error work.