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SpaceEngineer
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Spaceflight Physics Concept

29 Oct 2016 07:59

Last update: 29.10.2016

The Mothership

More information about the ship design is in the url=http://en.spaceengine.org/forum/14-69-1]Mothership concept[/url] thread.

The starship have two types of engines - the subluminal and superluminal. The first one is a conventional jet engines (fusion, ion, etc.) and used to change the physical speed of the ship, i.e. accelerate, decelerate, enter orbit etc. The second one is the Alcubierre warp drive and used for fast interstellar travel. The engines uses energy (e.g. electricity) produced in the main generator ('the core'). The core can be a dedicated fusion or antimatter reactor, but it can be also combined with the subluminal fusion engines - the MHD generator.

Subluminal engines

The ship uses a rocket (jet) engines for propulsion in the normal space. They are not a chemical of course, but some kind of fusion engines using D+T or D+3He fusion or antimatter annihilation as an energy source and hydrogen as a reactive mass (propellant). Note that they are different things, unlike chemical rockets.

The propulsion engines are very powerful and have a high exhaust velocity, they can speed up the ship at 10-20 G acceleration, and a ship has a characteristic speed (or delta-V) of up to 10,000 km/s from one refueling. The characteristic speed is the total ability of speed change. For example, deltaV = 1,000 km/s means that ship can accelerate to 50 km/s and break down 10 times. Only the most advanced ships in the game will have as large delta-V as 10,000 km/s. The propellant for the engines is hydrogen, water or something else, that can be easily mined in the space.

Refueling with hydrogen can be carried out during the flight through the atmosphere of a gas giant. The ship flies close to the gas giant at a certain speed, the air intake (ram scoop) opens in upper atmosphere and fills up the tank. A more profitable refueling can be done with a low-mass gas giants such as Neptune (they are called ice giants): such planets have a lower escape velocity, so a ship spends less hydrogen while departing from it. Large ships can have a special 'fuel bots' - smaller spacecraft designed specifically for hydrogen mining. Another option is to produce hydrogen from water or ice, which may be found on icy satellites or in comets.

Hydrogen in its liquid and solid phase has a very small density, so it needs a huge tank. For example, in the calculations provided below, the ship will need a 1,2-kilometers-wide tank, or 200 tanks with a diameter of 200 meters. Therefore, the game will use technology to store hydrogen in the so-called degenerate ('metallic') state, as in the depths of a gas giants. The density of hydrogen in this state is comparable to the density of water, and the diameter of a tank is reduced to 460 meters (or 12 tanks with a diameter of 200 meters).

Example calculation of mass and kinetic characteristics of the ship:
  • Size: diameter 400 m, length 1500 m
  • Mass without hydrogen: 1.5x1011 kg
  • Hydrogen mass: 6.0x1010 kg
  • Acceleration: 50 m/s2
  • Thrust: 7.5x1012 N
  • The characteristic velocity: 10 000 km/s
  • The exhaust velocity of hydrogen: 30 000 km/s
  • Hydrogen flow rate: 251 000 kg/s
  • The time of complete consumption of hydrogen: 2.7 days
  • The density of liquid hydrogen: 70 kg/m3
  • The diameter of the tank for liquid hydrogen: 1200 m (or 203 tank with a diameter of 200 m)
  • The density of metallic hydrogen: 1150 kg/m3
  • The diameter of the tank for metallic hydrogen: 460 m (or 12 tanks with a diameter of 200 m)

Superluminal engine

There game will use Alcubierre warp drive concept for faster than light travel. The warp-drive is a two large rings in front and tail of the ship, charged with negative energy. It is produced by the core (reactor) and accumulated in the rings. The warp drive performs as a multiplier applied to the physical velocity of the ship. The simple example: if the ship have a physical velocity of 100 km/s (relative to the 'vacuum' or Cosmic Microwave Background), engaging the warp drive with the warp factor of 1012 (or warp exponent of 12) will result in effective velocity of 100∙1012 km/s, or roughly 10 light-years per second. The typical maximum value of the warp exponent for a mid-sized ship is 12, so 10 ly/s is it's typical effective speed. It is possible to increase it simply by increasing the initial physical speed.

In the warp, the ship moves in the same direction where it's physical speed was pointed (the warp vector). So, to change the destination star/planet, you have to turn your physical velocity vector towards the new target, using the main engines. It is important to understand that this 'physical velocity' is measured relative to the 'space itself'. The Universe have a dedicated coordinate system which is related with the Cosmic Microwave Background radiation (CMBR). By measuring the dipole anisotropy in the CMBR spectrum, the ship's computer can compute it's physical speed. One can see what our Sun have a physical velocity of about 370 km/s towards the Leo constellation. This is mean that if you engage the warp drive while having a zero velocity relative to the Sun, you'll start warping towards the Leo constellation.

Such large physical velocity of the Sun means what reaching other stars with a warp drive become more complicated. Lets consider your are starting from the Solar System. If the star is located in the Leo constellation, you have to adjust the ship's physical velocity (warp vector) just a bit, but if a star is located in the opposite direction, you first must break down relative to the CMBR (370 km/s), then accelerate towards the destination star (to at least of some 10-20 km/s). So exploring stars near the direction of the current warp vector are much easy than the opposite ones.

The complexity is increased if we remember that planets and stars are moving relative to each other. Typical orbital speeds of a planets in the Solar System are 10-30 km/s, so their relative speeds may reach 20-60 km/s. Relative speeds of a nearby stars are 30-40 km/s. Thus once arrived to the destination planet, the ship will end up with some 30-100 km/s residual relative speed (assuming that you didn't change the physical speed too much for the warp). If there was a large change of the physical speed (like 370 km/s), you have to add this speed also (by vector sum). So ship must compensate (break from) this large speed to be able to enter an orbit around the planet.

The stars are revolving the center of the galaxy with a speeds of 200-250 km/s. So if you were decided to go to the opposite site of the galaxy, you will have the relative speed of the destination star of ~500 km/s. This will be added (as a vector) to the large change of the physical speed needed to perform warp in the right direction. This also means that such distant flight may require refueling of propellant (hydrogen) at some point, if the ship doesn't have the required delta-V ability. A flight to a distant galaxy certainly requires refueling, because relative velocities of galaxies may reach thousands of kilometers per second. For example, if the characteristic speed (delta-V) of the ship is 1000 km/s, and the destination galaxy is moving away from the departure galaxy at a speed of 10,000 km/s (due to expansion of the Universe), you will have to make ten intermediate stops at some galaxies along the way for refueling - this is the only way to reach a speed of 10,000 km/sec for this ship.

It's hard to start the warping from near the planet, because of it's gravitational influence. The gravitational pulling constantly attempts to change the physical velocity vector. So it's a good idea to warp away from the planet first, so it's gravity will no more influence the warp vector. Direction doesn't matter at this stage, simply engage the warp drive for a few seconds. Just make sure you will not crash into planet. Colliding of the warp bubble with a large mass will lead to collapse of the field, and ship will end up with a relative velocity which may point towards the obstacle.

In summary, to perform the warp, you must follow these steps:

1) Warp away from the nearby planet to some distance. Make sure you will not crash into planet while doing this.
2) Change your warp vector so it will point the target. Accelerate in a direction suggested by the ship's computer to do that more effectively.
3) Engage the warp drive and enjoy the interstellar flight.
4) While approaching the target, carefully reduce power of the warp drive, so you will not miss the target. Disable it completely at desired distance. Make sure your residual relative speed vector don't point to the target planet, otherwise you may have not enough time to decelerate!
5) Decelerate from the residual relative velocity to the orbital velocity, taking into account the vector math. Computer will help here.

Here is a modelling of interaction of interstellar dust particles or meteoroids with the warp bubble. Few particles are enters the bubble and hits the ship, so shield is required.
Open in new page

The landing craft

The Mothership is not designed to land on planets, so it carried several landing crafts (shuttles). The shuttle is a small spacecraft equipped with thermal rocket engines for flight in a vacuum and (possibly) a Ramjet/Scramjet for atmospheric flight. It does not have the warp drive. The ship uses an air from the planet's atmosphere for the atmospheric flight, and a propellant (hydrogen) stored in the on-board tanks for the space flight. The engines uses energy produced by the on-board energy generator (the same as the Mothership's). The shuttle can use some other working substance instead of hydrogen, including an air from an atmosphere.

There are two variants of shuttle design: the aircraft-like (for horizontal landing using aerodynamics) and the rocket-like (for vertical landing on its tail, as a classic sci-fi rocket ships).

The shuttle which is designed to land only on airless bodies always have a rocket design. It may be much lighter than the atmospheric shuttle, because airless bodies usually have a low gravity. They also do not require the aerodynamic shape. The atmospheric shuttle can land on airless bodies too, if it's rocket engines allow to do that (Ramjet cannot be used on airless bodies).

The aircraft design

The shuttle have an aircraft shape (similar to the US Space Shuttle): a horizontal design, with wings to create aerodynamic lift, with jet engines at the rear of the chassis and Ramjet on the wings or at the bottom of the hull.

  • Taking off. The ship can be launched from the surface in several ways: by using a special vertical take-off engines, or by rotating the main engines towards ground. After reaching some speed, it can engage the Ramjet, increasing its speed and altitude. The Ramjet uses the air as the propellant without spending hydrogen from the tanks, but it needs energy. In the upper atmosphere, where the velocity reaches 10-20% of the orbital velocity, the space (rocket) engines engages, and the ship reaches the orbital velocity. The rocket engines uses plenty of hydrogen stored in the tanks in the metallic form. By approaching the Mothership, the shuttle makes basic intercept manoeuvres and dock with it. The time between take-off and reaching the orbit is about 5-10 minutes (with acceleration of 2-3 G), but the basic intercept maneuver may require many hours and several orbital turns. However, in some cases, the Mothership can adjust its own orbit, or even use the warp drive to make a faster rendezvous with the shuttle.
  • Landing. The ship slows down its orbital velocity by using its space engines, then it enters the atmosphere at an acute angle (aerobraking). A descent flight through the atmosphere happens at hyper-sonic speed, resulting in the ship heating caused by air friction. The heat-shield at the bottom of the shuttle protects it from overheating. The shuttle reduces its speed using the air friction; to increase its efficiency, it can fly in wave-like motions, moving from left to right. When the speed drops below several times of the speed of sound, the Ramjet engages and the remaining flight to the landing zone is performed in aircraft mode. Landing can be carried out either by vertical take-off engines or by rotating the main engines towards ground.
  • Benefits. Usage of the Ramjet reduces the mass of the ship and the amount of hydrogen required for take-off. Flight in the atmosphere in aircraft mode does not consume hydrogen and is not limited by distance.
  • Weaknesses. Acceleration during take-off and orbital flight is directed 'back' (towards the engines), but during landing, atmospheric flight and when parked on the surface, it is directed 'down' (toward the ship's bottom). So it requires special internal planning. Aerobraking during landing leads to dangerous overheating, and a large distortion of the hull can destroy the ship. Taking off and landing without a runway is only possible by special vertical take-off engines or by rotating the main engines toward ground.

The rocket design

The shuttle have a shape of rocket. It have a vertical design, with small stabilizer wings at the tail with jet engines mounted near them. Stabilizers can also be used as a landing supports.

  • Taking off. The ship starts vertically, the same way as a conventional rocket do. In the initial stages of the flight, the ship may use Ramjet to save dome hydrogen. After reaching the upper atmosphere, this ship perform a course correction, so its flight path becomes more horizontal. From this position, the main jet engines will engages again, and the Ramjet is shut down. The space stage of the flight is the same as of the aircraft-design shuttle.
  • Landing. In contrast to the aircraft-design shuttle, this shuttle can not use aerobraking, its landing will be like launching in reverse. The ship breaks its orbital speed and enters the atmosphere with its tail directing forward, slowing itself down with jet engines at a relatively low speed, then gently touches the surface with its landing supports. The engines are firing during the final landing phase, so the ship must carry a greater amount of hydrogen, compared to the aircraft-design version.
  • Benefits. Acceleration at all stages is always directed 'downwards' (towards engines) - ideal for carrying passengers. The hull does not overheat during landing, if no aerobraking is used. Landing can be done on any solid surface. It can land and take off from any planetary body - with or without an atmosphere.
  • Weaknesses. It requires a greater amount of hydrogen in the on-board tanks, as compared with the aircraft-design version. Atmospheric manoeuvres are limited, because flight is only possible in rocket mode, which consumes many hydrogen.
 
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Juxlos
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Spaceflight Physics Concept

07 Nov 2016 12:25

SpaceEngineer wrote:
  • Size: diameter 400 m, length 1500 m
  • Mass without hydrogen: 1.5x1011 kg
  • Hydrogen mass: 6.0x1010 kg
  • Acceleration: 50 m/s2
  • Thrust: 7.5x1012 N
  • The characteristic velocity: 10 000 km/s
  • The exhaust velocity of hydrogen: 30 000 km/s
  • Hydrogen flow rate: 251 000 kg/s
  • The time of complete consumption of hydrogen: 2.7 days
  • The density of liquid hydrogen: 70 kg/m3
  • The diameter of the tank for liquid hydrogen: 1200 m (or 203 tank with a diameter of 200 m)
  • The density of metallic hydrogen: 1150 kg/m3
  • The diameter of the tank for metallic hydrogen: 460 m (or 12 tanks with a diameter of 200 m)

That's... quite a lot of power, isn't it?

[math]

Running a mothership needs 10 million times the current global energy consumption after accounting for all the energy you need to run SpaceEngine while on flight :p
Also, how would these things be constructed? I imagine making it on a planetary surface would be quite tricky.
 
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DoctorOfSpace
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Spaceflight Physics Concept

07 Nov 2016 18:31

Juxlos wrote:
Source of the post Also, how would these things be constructed? I imagine making it on a planetary surface would be quite tricky.

Orbital construction, considering the level of technology proposed this is not an issue.

Juxlos wrote:
Source of the post That's... quite a lot of power, isn't it?

Interstellar travel is expensive, no matter your level of technology it will require a lot of energy.
Check out this calculator
http://nathangeffen.webfactional.com/sp ... travel.php
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waterlubber
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Spaceflight Physics Concept

08 Nov 2016 18:35

A few small things.
Assuming I understand how you intend the warp drive to work, the Coriolis Effect will be a huge issue. Hopefully the computer can compensate.

For the engines, 10g of acceleration (92m/s^2) is pretty nuts. Even chemical rockets that guzzle fuel only have about 5g of acceleration with a reasonable mass ratio.

Of course, a torch drive would be equivalent to something like this, but you'd need inertial dampening.


Anyway, this all sounds awesome as I'd love a hard sci-fi game/
I remember the old forum!

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