Tag: Space Science in Practice

Digital Competition

Size and Scale in Space

Rescue missions in space are very different to Earth. Knowing how size and scale in space is like can help you design for this successfully.


by Neelesh Ravichandran, UKSDC Design & Publications Committee Chair


Where is everything?

Space is a vast expanse filled, mostly, with nothing at all. The diagram on the right of this article shows to scale: the Earth, the Moon and the distance between them.  Unlike in the movies where astronauts travel between planets in minutes, real space travel is a little bit slower than that.

The Apollo 11 mission to land on the Moon took three days to travel from its launch pad here on earth, to touch down on the surface of our moon. For those three days, the brave astronauts had to rely on their spaceship for all their needs. This ranged from food to sanitation, and really pushed the limits of 1960s technology.

How far are things from each other?

As we can already see, the moon is very far away from the Earth (384 thousand kilometres away to be exact). However, the distances to other planets are truly astronomical. In fact, the average distance between Earth and Mars is 362 million kilometres, which is a thousand times further than the Moon.

Everything in between Earth and Mars is just empty space, with the occasional asteroid floating through. Our Apollo crew would take a whole year to get from Earth to Mars, and that’s if they get lucky with the time of year that they launch from.

How long does space travel take?

Well it really depends on where you need to get to. If you’re designing a rescue craft that is meant to save people all across the solar system, you are going to need to design it to be lived in for years on end.

Some journeys can be made faster with advanced thruster technologies, that can make the spacecraft reach their destinations faster. Be careful though, the more powerful your thrusters the larger your fuel tanks need to be. This means to reach far away destinations quickly, your rescue craft will have to be equipped with powerful thrusters and large fuel tanks.

How do you design a spacecraft to keep working for years?

Spacecraft are very precise and powerful machines, but they can be fragile in space. Here, even a simple fleck of paint can punch a hole in a spaceship. So, to journey to the edges of the solar system and rescue stranded crews, your spaceship must be built robustly, with protections against small impacts from debris floating in space.

Food and water

If we want to keep our rescue crew alive for these long missions, we need to keep them fed and hydrated. Food can be dehydrated and kept very compact; this means that if you’d like you can pack enough food into your rescue ship for the whole journey.

Water is a more difficult resource to manage. You’ll have to carefully recycle all the water that your astronauts consume so that you don’t run out on your journey to the rescue site. It would be terrible if your rescue crew needed rescuing because they ran out of water!

Think of ways astronauts can reduce the water that they use, and how to recycle any water that might otherwise be wasted.

Navigation 

Keeping your spacecraft pointed in the right direction is a difficult task. Unlike on Earth where we can use a compass to tell where north is, in space there are fewer ways to really work out where you are.

You will need to design a way so that your spacecraft can work out where it is. It could use the stars to work out its location in the solar system, or it could even try contacting ground stations you have already installed on planets.

Rescue tool

When you are performing rescue missions in space, you might need some special tools to help you get to the stricken crew. This process might require your rescuers to perform spacewalks or cut into a broken spacecraft.

Make sure your spaceship is well equipped with the latest technologies and tools that can aid its operators to save the people who are in danger.

Let’s bring them home

We look forward to seeing how you are going design spacecraft that can travel through the vast expanses of space. We want to see how you’ve solved the challenges brought by long distance space exploration, and hope that your designs can help bring our crew home!


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Digital Competition

How Do Spaceships Move In Space?

Exploring the ins and outs of spacecraft flight control, focussing on the systems that control propulsion and orientation.


Written by Abdur-Raheem Kalam (Heemy), Galactic Challenge Volunteer 

Illustrated by Saffron Zainchkovskaya, Galactic Challenge Volunteer 


Moving around becomes surprisingly difficult when we enter space. How do spacecraft go forwards, backwards, side-to-side? What happens when we need to turn around? And if we start to veer off course, how do we nudge ourselves back into the right path? At its core, all these questions can be answered using that familiar textbook rule, Newton’s 3rd Law – for every action, there is an equal and opposite reaction. Apply a force in one direction, and you’ll move in the other. Despite how crucial this fundamental law is to space flight, it still leaves some holes in our understanding of movement in space, holes which we need to fill.

Let’s think about a moving spaceship, hurtling through the Kuiper Belt on its way to Halley’s comet. We can describe the spaceship’s movement as a vector (specifically, as velocity) – that is, a property describing (1) the spaceship’s speed, and (2) the direction in which it travels. Therefore, by changing our spaceship’s velocity, we can move our spaceship in any direction and speed of our choosing – all we need is to vary these two variables. To achieve this, we require full, accurate and reliable systems of controlling speed and direction. It is these systems of control that underpin the flight and manoeuvres of our spaceship.

Controlling Speed

For us to control speed, engineers design a propulsion system. The propulsion system is what is most commonly associated with space flight – it’s the thrusters at the back of the spaceship that move the spaceship forward. They do this by expelling material out of the engine, in doing so generating a force that accelerates the rocket forward (starting off slow, but building up speed over time).

There are two main types of spacecraft propulsion systems – chemical and electric. Chemical propulsion involves burning a fuel to produce thrust. Take two elements, hydrogen and oxygen. These are combusted (burnt) together, undergoing a chemical reaction, forming water whilst releasing heat. The water consequently heats up, evaporating into steam. These water particles move further apart, causing the gas to expand until it pushes outwards on the fuel chamber. The inside pressure forces the gas outwards at a high velocity from the nozzle of the thruster, producing thrust. This process is shown in three stages below:

Alternatively, electric propulsion systems use electric and magnetic processes to shoot fuel out of a rocket, thus producing thrust. One of the simplest forms of electric spacecraft propulsion is a pulsed plasma thruster (PPT), otherwise known as a plasma jet engine. In the engine chamber, propellant (normally a solid) is converted into plasma (a gas cloud, filled with charged particles). On either side of the chamber are two electrically-charged plates, one positive, the other negative (a bit like either end of a battery). This gas cloud lies in between them. As the plasma’s particles are charged and able to move around, they are able to act as a bridge between the two charged plates, completing the circuit, like a wire connecting the two sides of the battery together. A complete circuit allows charged electrons to flow. This flow (and its consequent magnetic effects) results in our plasma being accelerated out of the PPT exhaust, at an incredibly high velocity (like this). The ‘pulse’ in PPT comes from the time taken to recharge, following each burst of propulsion (however, these pulses occur in very quick succession, so our spaceship’s movement is smooth, not jolty). Controlling our PPT allows us to control speed. This propels the spacecraft forward through space.

Changing Direction

That’s speed sorted – but how do we change direction? For us to control this, we have to control the orientation of the spaceship – this is what our spaceship’s attitude control system deals with. Attitude manoeuvres, sometimes known as roll/pitch/yaw manoeuvres (as outlined in the diagram below), involve making precise, fine adjustments to the direction a spaceship faces. 

This is achieved through use of smaller thrusters (known as vernier thrusters), which are strategically positioned around the aircraft, to exert the desirable level of torque (or spinning power) when in use (also visible in the diagram below). Some combination of roll, pitch and yaw manoeuvres will allow us to rotate our spaceship into any desired position. 

To power our vernier thrusters, we can use a chemical called hydrazine. We use this chemical as it is extremely reactive – it’s so reactive, it spontaneously sets itself alight when it comes into contact with certain chemicals! This makes it incredibly useful – it can release a large amount of energy without us having to heat our fuel to a high temperature, saving a lot of energy/fuel, whilst still providing the desired thrust for attitude manoeuvres. (SpaceX uses hydrazine in some of their thruster designs, for this reason). If we wanted to change orientation, we would input our desired change into the spaceship’s computer. Our computer would then control the firing of specific vernier thrusters at specific intensities (kept in-sync using special computer algorithms), and the spaceship would rotate accordingly, enabling us to make fine adjustments to the direction a spaceship faces.

Examples of Manoeuvres

We can now fully control our spaceship’s flight path – we can vary speed and direction. So what can we do with this? Here are two advanced, frequently used manoeuvres, which can help deal with changes in the flight path of a spaceship:

  • Trajectory Control Manoeuvers (TCMs) are used to adjust the flight path (pre-planned spaceship journey) of a space mission. They are conducted after or before a ship reaches an important milestone of its mission, like reaching the orbit of a planet. This is an important measure to take, as these precise adjustments make up for the small errors that add up over a spaceship’s journey, ensuring that our spaceship will stay on track in its path to Halley’s comet. Our attitude control systems are critical to TCMs.
  • A larger form of a TCM is a Deep Space Manoeuver (DSM). These manoeuvres (changes in direction) are controlled by the control systems mentioned earlier, only the manoeuvres are generally much bigger (opposed to the small adjustments undergone in TCMs).

More complex manoeuvres can be used to change how and at what speed our spaceship orbits a planet or outer space body. These manoeuvres take into account the impact of gravity on the spaceship. This set of manoeuvres (known as orbital manoeuvres) requires a strong understanding of a field of physics called orbital mechanics, but like TCMs and DSMs, fundamentally involve the same primary propulsion and attitude control systems that we previously mentioned.


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