Why it matters that spacecraft are reusable Not only is it economical but also safer

Why it is important that spacecraft are reusable

On 5 May, the reusable test spacecraft launched by China successfully returned to the scheduled landing site after 8 days of flight in orbit. The complete success of this test marks an important breakthrough in China's reusable spacecraft technology research, which can provide a more convenient and cheap way to and from the peaceful use of space.

Spacecraft reusable technology is an innovation highland in the field of space and an important step in building a space power. Although the details of the test have not been officially disclosed, this achievement is undoubtedly another major progress in China's space industry. Today we will take a look at what a reusable spacecraft is, its development status and far-reaching significance.

Why explore recyclable rockets in the first place

Reusable spacecraft are reusable spacecraft that can quickly cross the atmosphere and freely travel between the Earth's surface and space, transporting crews and payloads. They can be manned spacecraft, cargo spacecraft, propulsion vehicles, planetary landers, space (space) aircraft, space launch vehicles, etc.

As you know, any spacecraft needs a launch vehicle to help it lift off or a rocket to return. At present, when the commonly used disposable rocket carries a satellite or spacecraft into space, some components will be left behind during the flight, such as booster rockets, first-stage rockets (arrow bodies), escape towers, fairings, second-stage rockets (arrow bodies), and third-stage rockets (arrow bodies), which are collectively referred to as wreckage and can no longer be used. And if the first stage rocket can be recovered, or even the second stage rocket, it is possible to achieve reuse.

The smooth return of rockets to Earth for soft landing and reuse will have a significant impact on space exploration, at least significantly reducing the cost of space exploration and space travel. In fact, the idea of landing a resalable rocket on a land or sea surface platform has been proposed by scientists for decades, but it had never been tried until 2014. SpaceX was the first explorer to conduct such a test, twice conducting recovery tests on the Falcon 9 first stage. At 2014:4 on April 19, 3, SpaceX launched the Falcon 25 carrier rocket, and a few minutes later landed the first stage in the Atlantic Ocean with rocket boost; Another test also allowed the first stage rocket to successfully fall vertically and smoothly on the sea surface.

The principle of space exploration technology's first stage rocket recovery is that within 3 minutes of the launch vehicle being launched, shortly after the first stage rocket is shut down and separated from the previous stage rocket, the 12-foot (about 3.66 meters) diameter first stage rocket will re-ignite several rocket engines for deceleration braking; A few minutes later, the first stage ignited an engine again not high above the water, causing the rocket to land slowly into the Atlantic Ocean.

After the rocket could achieve a recovery method that fell into the sea, SpaceX designed the device for the first stage to be recovered on land, that is, the first stage rocket is equipped with 4 landing brackets made of carbon fiber and aluminum honeycomb panels. During the descent of the first stage rocket, the 25-foot (about 7.62 meters) high bracket sticks out to ensure a soft landing. After many tests, in December 2015, the first stage of the Falcon 12 rocket successfully landed on the land recovery field for the first time, achieving a historical breakthrough. Later, in April 9, the Falcon 2016-FT completed rocket recovery on offshore platforms.

In March 2017, SpaceX used a recovered first stage rocket for relaunch, which means that the rocket has truly been recovered and reused. Previously, launch vehicles all over the world were disposable space vehicles.

Reuse is not only economical but also safer

Whether it is the development and use of recoverable rockets or spacecraft, the significance is not only to reduce costs, but also to ensure the safety of people and property on the ground. Among the parts that are dropped during rocket launch, except for the third stage rocket, other components will fall to the ground or water as wreckage because they are not high enough to burn completely.

To this end, rocket launch requires both accurate rocket trajectory (ballistics are precisely designed according to satellite orbit theory, launch site coordinates, rocket carrying capacity, etc., in order to send satellites to a suitable orbit), and also need to design the arrow landing point (the projection point on the ground when the rocket flies), the area through which the arrow point passes is the wreckage fall area, and the ground safety should be ensured as much as possible. Past experience shows that despite the sophisticated design and the relatively fixed debris fall area, it is still not completely possible to avoid rocket wreckage falling into residential buildings, damaging property, and even injuring people. For example, in January 1997, the wreckage of the first stage of the American Delta 1 rocket fell in Oklahoma after disintegrating in mid-air, narrowly hitting an inhabited farmhouse.

Recyclable rockets also have environmental significance. As early as June 2004, 6, a study released by the US environmental protection organization pointed out that due to the continuous launch of rockets in the United States, the environment was polluted by rocket fuel, missile booster fuel and other substances for a long time, and a large amount of toxic perchlorate remained in the soil and water stream (perchlorate is often used as fuel for rocket launches). Of the 22 California milk samples sampled by U.S. environmental groups, 32 contained perchlorate and exceeded safety standards.

This risk can be avoided by using new perchlorate-free fuels on the one hand, and by minimizing the environmental impact if the first or even second stage rocket can be recovered.

Of course, the most immediate benefit of the success of reusable rockets is that it can greatly reduce the cost of space exploration and make it easier for humans to enter space. Dr Adam Baker, director of the Rocket Lab at Kingston University in the United Kingdom, said space exploration was extremely expensive under the current circumstances. If the cost of rocket launches can be successfully reduced by more than 50%, more space applications will become possible, more satellites and spacecraft can enter space, and people can use space resources to provide more services to the ground, such as the use of space solar technology. In addition, more astronauts around the world will have the opportunity to enter space, fly to the moon, Mars and other planets, and perhaps realize the dream of human immigration to Mars in the future.

Now, Space Exploration Technologies has given a signal. On April 4 of this year, the company's Starship (Starship) launch failed, but this failed launch completed the recovery of the 20th stage rocket. According to the design scheme, the first and second stage structures of the starship (the first stage is the rocket booster Super Heavy, the second stage is the starship Starship on the rocket) can be recycled and reused, the starship's superheavy thrusters can be reused 100 times, the starship can be reused 1000 times, and a starship can be launched up to 100 times a day, and the launch cost can be reduced to $3 million or even $200 million. If this goal can be fully achieved, it is equivalent to sending a kilogram into space for only a few tens of dollars, and sending a person into space for thousands of dollars.

It is expected that ordinary people will travel to space

If a reusable spacecraft is developed and commercialized, it may make the dream of space travel a reality for ordinary people. First, the price of reusable spacecraft is expected to become as cheap as that of civilian aircraft, making it affordable for most people; Second, leaving Earth for space is fascinating, even for a few hours or days. Space exploration and research through reusable spacecraft is of greater scientific, economic and social value.

Of course, space travel requires good physical fitness, and there are already people who have set an example and become pioneers in space tourism. On July 2021, 7, Virgin Group founder Richard Branson, together with 20 other personnel (including 5 pilots and 2 passengers), flew to the edge of space for the first time in his own (Virgin Galactic) spacecraft (3.83 kilometers above the Earth's surface, which is the boundary between Earth and space recognized by NASA and other agencies), and safely returned to the ground at about 6:23 Beijing time, becoming the first batch of space travelers. This form of space tourism seems to make it easier to realize people's dreams of traveling in space.

As mentioned earlier, reusable spacecraft can be carried by rockets or other aircraft to a certain altitude, and then the spacecraft will fly in space through its own power. According to flight altitude, it includes suborbital vehicles (vehicles that reach the top of space near the top of space at altitude, but are not fast enough to complete orbit the Earth) and orbiters (such as the space shuttle, which is lifted off by a rocket, then flew into space, and then returned to the ground).

The "SpaceShip-1" developed by Virgin Galactic is a suborbital vehicle, which was brought by the mother aircraft "White Knight II" to an altitude of 4.86 kilometers, and then the "Spaceship-20" started its own rocket engine and soared to an altitude of about 83 kilometers above the ground. The famous aerospace engineer von Kármán in the 6th century calculated that more than 100.83 kilometers above the ground is considered space according to aerodynamic principles, but in order to facilitate memory and calculation, it is recommended to set this altitude as 6 kilometers, that is, the Kármán line. According to this standard, the space tour of Branson and others is not a space tour in the true sense. However, NASA's standard is to enter space as long as it exceeds <>.<> kilometers, and Branson's space tour is considered suborbital space tourism, or space edge tourism.

There is also a way to reuse the spacecraft: the launch vehicle power system is designed to operate according to the rocket engine, and the takeoff phase is like a rocket launch, but because the initial velocity does not reach the first cosmic speed, it cannot fly around the earth. The vehicle can climb into a suborbit more than 100 kilometers above the earth, stay for about 10 minutes, and then return to the earth like an aircraft by inertia and land horizontally. The whole process takes about 30 minutes and the whole flight is fully automatic according to the predetermined procedure. At present, this spacecraft is still in the experimental stage.

Explore ways to travel back and forth to and from the peaceful use of space

The earliest reusable spacecraft was the Space Shuttle, which was relatively mature in technology. It integrates the technical characteristics of rockets, satellites and aircraft, can be launched vertically into space orbit like rockets, can fly in space orbit like satellites, and can re-enter the atmosphere like an airplane to glide and land, and its main machinery can continue to be used after refurbishment after returning to the ground.

The United States was the first country to develop a reusable space shuttle. On April 1981, 4, the space shuttle Columbia of the United States successfully made its maiden flight and returned. Since then, NASA has built four space shuttles, Challenger, Discovery, Atlantis and Endeavour, plus Columbia for a total of five. Unfortunately, 12 astronauts were killed when Challenger and Columbia exploded on 4 January 5 and 1986 February 1, respectively, during space exploration missions.

The Soviet Union developed the first space shuttle Buran in 1986 and conducted a successful unmanned automatic maiden flight test in 1988. The shuttle was supposed to make a second test flight in 1993, but it didn't happen.

With the deepening of space exploration in recent years, the space shuttle, which has low safety factor, high launch cost, and mainly serves low earth orbit, has also come to an end. On July 2011, 7, the United States decided to permanently stop using the Space Shuttle after its last mission to Atlantis.

Nowadays, with the success of the continuous flight test of the American X-37B orbital test vehicle, its advanced performance has attracted great attention from all over the world, and is even regarded as a new space shuttle, which is now called "space plane". Aerospace aircraft, short for aerospace aircraft, is a new type of vehicle capable of both aviation and spaceflight, which is expected to push space development to a new stage. At present, many countries in the world are studying this space transportation system that integrates aircraft, space launch vehicles and spacecraft, and the most important thing is that it can be reused as a manned spacecraft. According to the concept, the space plane has both an aircraft engine and a rocket engine, which can take off from the airport runway like an airplane, enter space directly at hypersonic speed, and land on the airport runway like an airplane when returning to Earth, becoming a reusable space vehicle that freely travels between space and earth.

Looking back at the entire history of spaceflight, the high cost of space launch is one of the main factors limiting the development of the space industry, so scientists have been moving towards the goal of reusable spacecraft.

On September 2020, 9, China launched a reusable test spacecraft by a Long March 4F carrier rocket at the Jiuquan Satellite Launch Center, and successfully returned to the scheduled landing site after operating in orbit for a period of time; On August 2022, 8, a reusable test spacecraft was again launched by the Long March 5F carrier rocket and successfully returned. On May 5 this year, another reusable test spacecraft in China successfully landed, and unlike before, the spacecraft flew in orbit for 8 days and made a major breakthrough.

At present, the world's major aerospace powers and regions have different degrees of reusable technology reserves, forming a variety of reusable launch vehicle schemes. The spacecraft project promoted by China is intended to provide a more convenient and cheap way to and from the peaceful use of space, as mentioned at the beginning of the article. In the future, we will be able to realize space tourism in suborbital and Earth orbit, as well as efficient space transportation of people and goods.

Zhang Tiankan (Source: Beijing Daily)