Realistic Space Travel

When speaking of space travel, it is important to distinguish interplanetary travel from interstellar travel. Travel between planets is within the grasp of modern technology and is likely to become easier as science develops new fuel sources or new ways to maximise existing fuel sources. Travel between stars, on the other hand, calls for some truly radical leaps in a number of different fields.

Hazards of Space Travel

Space travel is nowhere near as easy as books and movies make it seem. Foreign objects are a constant danger; even a micro meteoroid travelling at a high enough velocity can punch a hole through a starship's hull and expose the entire crew to the vacuum of space. Ionising radiation also poses a serious threat. Finally, characters must adapt to the weightlessness of space or suffer the effects of space adaptation syndrome (SAS), referred to colloquially as "space sickness."

Meteoroids

Meteoroids are small rocks that travel through space at a speed of 7 miles per second. They can be as small as a grain of sand or as big as a mountain. Although they generally burn up in a planet's atmosphere before reaching the ground, meteoroids in space aren't likely to suffer such a fate. Instead, they slam into other objects, including starships and space stations, like volleys of rifle or artillery fire.

Unarmoured starships and space stations can easily survive impacts from the smaller meteoroids, but larger ones can punch lethal holes in such fragile vessels. Fortunately, large meteoroids are rare and easier to detect before they can get too close to cause any real damage.

Roll on table Meteoroid Encounters to determine whether a meteoroid threatens a given starship or space station. Each roll represents one 24-hour period.

Size: The size of the meteoroid.

Dam: When a meteoroid collides with a starship, space station, or other object, both the meteoroid and the object it strikes take damage.

Computer Use: A starship or space station equipped with a sensor system can detect an incoming meteoroid; doing so requires a successful Computer Use check. A starship or space station cannot attempt to avoid or destroy a meteoroid it fails to detect.

Pilot: Avoiding a meteoroid requires a successful Pilot check. Only starships or space stations that move are capable of avoiding meteoroids.

Def: The meteoroid's Defense.

Hard: The meteoroid's hardness.

HP: The meteoroid's total hit points.

Meteoroid Encounters

d%	Size	Dam	Computer Use	Pilot	Def	Hard	HP
01-75	No meteoroid
76-80	Diminutive	1d6	35	5	9	8	15
81-85	Tiny	2d6	30	10	7	8	30
86-88	Small	3d6	25	15	6	8	90
89-91	Medium-size	4d6	20	20	5	8	225
92-94	Large	1d6x5	15	25	4	8	1,125
95-97	Huge	3d6x5	10	30	3	8	4,500
98-99	Gargantuan	6d6x5	5	35	1	8	9,000
100	Colossal	12d6x5	0	40	3	8	36,000

Both the meteoroid and the object it strikes take damage from the collision.

Vacuum Exposure

Beings exposed to the airless cold of space are not immediately doomed. Contrary to popular belief, characters exposed to vacuum do not immediately freeze or explode, and their blood does not boil in their veins. While space is very cold, heat does not transfer away from a body that quickly. The real danger comes from suffocation and ionising radiation.

For rules on vacuum exposure and the effects of weightlessness, see Atmospheric Conditions and Gravity in the Environments section.

Radiation

Ionising radiation is common in space. For the effects, see Radiation Sickness in the Environments section.

Reentry

Anything that travels too fast in an atmosphere generates an enormous amount of friction, which produces tremendous heat. (Temperatures of 2,280 degrees Fahrenheit have been recorded.) Objects trying to enter a planetary atmosphere safely must shed velocity. However, decelerating consumes large amounts of fuel, and many ships (especially at Progress Level 5) simply don't have enough. As an alternative, scientists have developed ways to slow ships in reentry by using the atmospheric friction itself. Ablative shielding or ceramic tiles take care of any excess heat. Even so, entering a planet's atmosphere is a tricky business; the angle of entry is precise, and deviation either way causes the heat to build up too quickly for the heat shields to reflect away from the ship. Worse yet, during the most intense heating, the ship is surrounded by a thin layer of plasma that blocks radio signals, and the crew have no contact with ground control.

Entering planetary atmosphere safely requires a Pilot check (DC 20) each round for the 1d10+20 rounds it takes to slow the ship using friction alone. Success means that the ship takes only 3d6 points of fire damage each round. Failure means that the ship's angle is too low, and that it is not shedding velocity fast enough; the ship takes 6d6 points of fire damage each round until the pilot succeeds at the Pilot check to correct the angle of descent. If the check fails by 5 or more, the angle is too steep, and the ship takes 10d6 points of fire damage each round until the pilot succeeds at the Pilot check to correct the angle. Each round spent at too low an angle does not count toward the number of rounds required to land the ship; the ship isn't making any downward progress. Conversely, each round spent at too steep an angle counts as 2 rounds, indicating that the ship is descending much faster than it should.

Interplanetary Travel

In Progress Level 5, humanity has the technology to send unmanned probes to the edge of the solar system. However, human sojourns into space are limited to orbital missions and trips to the Moon, as longer journeys would take decades and consume ridiculous amounts of fuel and oxygen.

Interplanetary travel becomes possible at Progress Level 6. Ships fitted with magnetic ram scoops allow the crew to manufacture fuel from particles of hydrogen gas floating loose in space (though at only a few atoms per cubic inch). Such a ship could even incorporate a particle accelerator that converts matter into antimatter with far more efficient thrust-to-payload ratios than solid fuel. With a sufficient supply of food, water, and oxygen, a ship so equipped could travel to the edges of the solar system and perhaps to another solar system entirely.

Interstellar Travel

Realistically, the starships presented in the Starships section are capable only of interplanetary travel, not interstellar travel. The reason for this is simple: Even the best engine can't accelerate a ship to light speed, and without light speed, interstellar journeys take tens of thousands of years. The speed of light is 186,000 miles per second. That's 1,116,000 miles per round, or 66,960,000 miles per hour. Manoeuvring a ship at this speed is a tricky proposition; by the time you notice an object in your path, it's probably too late to avoid it. One must also consider relativity: The closer the ship's velocity comes to the speed of light, the greater its mass. A starship cannot achieve light speed via simple acceleration, no matter how powerful the ship's engine, as increasing the power only increases the mass.

The greatest impediment to travelling between the stars is time: What would be the point of sending astronauts to Alpha Centauri, for example, if, by the time they arrived, no one on Earth could remember why they'd gone in the first place? Time dilation the slowing of the passage of time in relation to an object travelling at close to the speed of light becomes a factor. A few years might pass on board the ship, while a few hundred years might have passed both at the ship's point of origin and its point of arrival.

Realistic Travel Times

The table: Realistic Travel Times provides various "realistic" interplanetary and interstellar travel times. These times assume that starships cannot achieve velocities anywhere near the speed of light, for reasons discussed under Interstellar Travel (see above). Using the table, a starship equipped with a PL 6 ion engine would take 67.2 days to travel from Earth to Mars, while the same ship equipped with a PL 7 induction engine would take 16.8 days.

The travel times listed are based on average distance. Planets move closer together and farther apart based on their relative orbits around the sun, and the travel time between worlds may increase or decrease accordingly.

Time Dilation

When a ship approaches to within 90% of the speed of light, time slows down. Characters on board the ship would not notice, but if they were to make hourly reports back to their point of origin, those reports might arrive only once every hundred hours.

This creates an interesting paradox, in that if a character managed to travel at the speed of light to another star and back again, a newborn child he left behind would now be older than him if the child hadn't died of old age some time ago.

The actual amount of time dilation observed aboard a ship travelling near light speed increases in proportion to just how close it is to light speed. Technically, time dilation occurs at any speed, but it only becomes noticeable at relativistic speeds. The dilation is a ratio that determines how much time passes aboard the ship; it is a multiplier when determining how much time passes outside the ship.

For example, a ship moving at 70% the speed of light has a time dilation of 1.4. Ten hours of travel aboard the ship at this speed means that 14 hours (10 × 1.4) have passed outside the ship. However, if ten hours pass for those left behind, only 7.1 hours have passed aboard the ship (10 divided by 1.4).

Time Dilation

Starship Speed (miles/second)	AU per hour	% Speed of Light	Time Dilation
2,046	0.18	1.1%	1.0003
26,040	1.0	14%	1.01
52,080	2.0	28%	1.04
78,120	3.0	42%	1.1
104,160	4.0	56%	1.2
130,200	5.0	70%	1.4
154,380	6.0	83%	1.8
167,400	6.5	90%	2.3
180,420	7.0	97%	3.9
182,466	7.1	98.1%	5.1
185,981	7.239	99.99%	60.2

Starship Speed: The vessel's speed in miles per second.

AU per Hour: How many Astronomical Units (AU) a vessel travelling at this speed can cross in 1 hour. One AU equals 93,000,000 miles (the distance between the Sun and the Earth).

% Speed of Light: The percentage of the speed of light (186,000 miles per second).

Time Dilation: Divide the time travelled by this number to arrive at the amount of time that passes on board the starship.