Original post by User:Ophadamious
Celestial bodies have their own difficulty to get there.
We'll tag difficulty by 3 categories:
- Easy
- Medium
- Hard
For example, Mars is easy because it is near to Earth, after the Moon and Venus and low gravity. Ganymede is hard due to the high delta-v requirement, its terrain and high gravity.
Note that we will use the Delta v template a few times in each section to get how much fuel is required to get to a celestial body.
Difficulties[]
Flyby[]
Mercury[]
DIFFICULTY: MEDIUM
Mercury can be an interesting target for flybys directly from Earth; but due to the high delta-v requirement of 1.1 km/s, it is a little difficult to do it.
If you are in a lower heliocentric orbit the amount of fuel will be much lower, thus decreasing the category to EASY.
Venus[]
DIFFICULTY: EASY
Venus is relatively close to Earth, so a flyby can be conducted there with limited data. A Venus flyby can be used for raising the orbit to Mars or beyond or lowering the orbit to Mercury or closer.
Moon[]
DIFFICULTY: EASY
The moon can be used for a free-return trajectory (impacting earth) (just like the Apollo missions did) or an earth escape trajectory (to get to a heliocentric orbit that intersects Earth).
Mars[]
DIFFICULTY: EASY
Mars flybys can be used for small gravity assists to push the trajectory to Earth or the asteroid belt. When in a lower heliocentric orbit, the effect is much smaller; now we will raise the category to MEDIUM.
Jupiter[]
DIFFICULTY: EASY
Jupiter can be used for gravity assists for boosting rockets to the interstellar void or a lower heliocentric orbit. However, the "curve" of the trajectory can be really sharp, so set the perijove to a higher level, especially at around the orbit of Europa or Ganymede.
Orbit[]
High orbit[]
Note: We won't list some celestial bodies in this section because high orbits on some celestial bodies intersect outside their sphere of influence or aren't commonly used.
Mercury[]
DIFFICULTY: HARD
Directly from Earth, approaching Mercury without gravity assists can require a lot of fuel. Look at the delta-v chart below:
| Destination | Delta-v required (m/s) |
|---|---|
| Low earth orbit (starting point) | 1665 |
| Earth orbit (550 km) | ??? |
| Moon | 665 |
| Moon orbit | 820 |
| Earth escape | 681 |
| Mars transfer | 765 |
| Mars orbit | 1205 |
| Phobos orbit | 1110 |
| Deimos orbit | 1040 |
| Venus transfer | 740 |
| Venus orbit | 1435 |
| Direct Mercury transfer | 1120 |
| Mercury orbit | 2705 |
| Jupiter transfer | 1335 |
| Callisto | 2675 |
| Ganymede | 3020 |
| Europa | 3552 |
| Io | 3855 |
| Low Jupiter orbit | 5200 |
| Interstellar travel (no gravity assists) | 1850+ |
As you can see, a Mercury orbit with no assists requires 2.7 km/s of delta-v. To lower the delta-v requirement, it is recommended to use some orbital techniques to get there. Getting to high orbit directly requires lower velocity making the delta-v much higher.
It is recommended to get to low orbit, then transfer to high orbit.
Venus[]
DIFFICULTY: MEDIUM
Directly from Earth, a Venus encounter with a high periapsis then burning there at the periapsis can have a higher cost. It is recommended to get on a low orbit, then a Hohmann transfer to the high orbit.
Earth[]
DIFFICULTY: EASY
Earth is home to the geostationary orbit that has an altitude of ≈550 kilometers. It is easy to get there from LEO.
To get to geostationary orbit, you need to burn prograde until the apogee gets to 550 kilometers. Do the second burn at the apogee by burning prograde until the trajectory is roughly circular.
Moon[]
DIFFICULTY: EASY
A high orbit on the moon is relatively easy because the delta-v requirement is relatively low. Space stations can be positioned in this orbit, sometimes at eccentric orbits.
Mars[]
DIFFICULTY: EASY
A high orbit on Mars requires some fuel but not too much. High orbits on Mars get past the orbit of Phobos.
Jupiter[]
DIFFICULTY: EASY
A high orbit on Jupiter is very common for orbiters because of the low radiation levels. It is cheap to get to a high/eccentric orbit around Jupiter, because of the low delta v requirement.
Low orbit[]
Mercury[]
DIFFICULTY: HARD
On Mercury, orbiting it directly from Earth is very difficult because of the high delta-v requirement. Here's the chart, again...
| Destination | Delta-v required (m/s) |
|---|---|
| Low earth orbit (starting point) | 1665 |
| Earth orbit (550 km) | ??? |
| Moon | 665 |
| Moon orbit | 820 |
| Earth escape | 681 |
| Mars transfer | 765 |
| Mars orbit | 1205 |
| Phobos orbit | 1110 |
| Deimos orbit | 1040 |
| Venus transfer | 740 |
| Venus orbit | 1435 |
| Direct Mercury transfer | 1120 |
| Mercury orbit | 2705 |
| Jupiter transfer | 1335 |
| Callisto | 2675 |
| Ganymede | 3020 |
| Europa | 3552 |
| Io | 3855 |
| Low Jupiter orbit | 5200 |
| Interstellar travel (no gravity assists) | 1850+ |
A Mercury orbit uses around 2.7 km/s of fuel directly from Earth; so you need a large rocket or docking rocket stages to get there.
A low-fuel method can be used. The answer — gravity assists. When the rocket finally intersects Mercury's orbit, and makes a transfer burn, the delta-v requirement is now drastically lower.
Venus[]
DIFFICULTY: MEDIUM
A low Venus orbit can require some fuel — but not too much. Let's open the chart, now for the third time...
| Destination | Delta-v required (m/s) |
|---|---|
| Low earth orbit (starting point) | 1665 |
| Earth orbit (550 km) | ??? |
| Moon | 665 |
| Moon orbit | 820 |
| Earth escape | 681 |
| Mars transfer | 765 |
| Mars orbit | 1205 |
| Phobos orbit | 1110 |
| Deimos orbit | 1040 |
| Venus transfer | 740 |
| Venus orbit | 1435 |
| Direct Mercury transfer | 1120 |
| Mercury orbit | 2705 |
| Jupiter transfer | 1335 |
| Callisto | 2675 |
| Ganymede | 3020 |
| Europa | 3552 |
| Io | 3855 |
| Low Jupiter orbit | 5200 |
| Interstellar travel (no gravity assists) | 1850+ |
A Venus orbit requires 1.44 km/s of delta-v, lower than getting to Earth orbit — so it's important to pack up some extra fuel in your Venus lander, but not too much.
Earth[]
DIFFICULTY: EASY
Earth is the starting point for most rockets launching to space. Their first destination is a parking orbit around the Earth. It requires around 1.7 km/s of fuel to get to orbit around the Earth.
Many rockets require 2 or 3 stages to get to orbit; some rockets like the Ariane 5 and the SLS need only one stage to get to orbit; therefore, they are called SSTOs, or Single Stage to Orbit rockets.
Moon[]
DIFFICULTY: EASY
Orbiting the moon from Earth orbit requires low delta-v. Let's open the chart again:
| Destination | Delta-v required (m/s) |
|---|---|
| Low earth orbit (starting point) | 1665 |
| Earth orbit (550 km) | ??? |
| Moon | 665 |
| Moon orbit | 820 |
| Earth escape | 681 |
| Mars transfer | 765 |
| Mars orbit | 1205 |
| Phobos orbit | 1110 |
| Deimos orbit | 1040 |
| Venus transfer | 740 |
| Venus orbit | 1435 |
| Direct Mercury transfer | 1120 |
| Mercury orbit | 2705 |
| Jupiter transfer | 1335 |
| Callisto | 2675 |
| Ganymede | 3020 |
| Europa | 3552 |
| Io | 3855 |
| Low Jupiter orbit | 5200 |
| Interstellar travel (no gravity assists) | 1850+ |
As you can see, orbiting the moon requires 825 m/s of delta-v. This is lower than getting to orbit on Mars. That means a 2-stage rocket can get there.
Mars[]
DIFFICULTY: EASY
Getting to Mars orbit requires low fuel, at 1.2 km/s. That means a 2-stage rocket can probably get there, if it has enough fuel.
The small size and low gravity of Mars means that it is easy to get to orbit and land on it; however, if you are positioned in a low heliocentric orbit, the amount of fuel is much higher, so let's raise the category to HARD.
Mars's moons[]
DIFFICULTY: EASY
Getting to Mars's moons are easy. You position in a low orbit on Mars, then you transfer to one of the moons (Phobos; Deimos). The delta-v is lower when positioned in a higher orbit.
When encountering the moons, the rocket will have a high velocity (<100 m/s), and probably freeze by exiting the moon's sphere of influence; so it is recommended to do the insertion burn before getting to the periapsis, right after entering their sphere of influence.
Getting to Deimos is easier than getting to Phobos because it is farther from Mars and its large sphere of influence.
Jupiter[]
DIFFICULTY: HARD
Getting to a low Jupiter orbit is the most fuel-consuming mission in Spaceflight Simulator. Let's look at the delta-v chart below for the fifth time:
| Destination | Delta-v required (m/s) |
|---|---|
| Low earth orbit (starting point) | 1665 |
| Earth orbit (550 km) | ??? |
| Moon | 665 |
| Moon orbit | 820 |
| Earth escape | 681 |
| Mars transfer | 765 |
| Mars orbit | 1205 |
| Phobos orbit | 1110 |
| Deimos orbit | 1040 |
| Venus transfer | 740 |
| Venus orbit | 1435 |
| Direct Mercury transfer | 1120 |
| Mercury orbit | 2705 |
| Jupiter transfer | 1335 |
| Callisto | 2675 |
| Ganymede | 3020 |
| Europa | 3552 |
| Io | 3855 |
| Low Jupiter orbit | 5200 |
| Interstellar travel (no gravity assists) | 1850+ |
In the chart, a low Jupiter orbit requires around 5.2 km/s. The reason behind this is its gravity and size.
Galilean moons[]
DIFFICULTY: Depends on celestial body
Getting to the Galilean moons can depend on the terrain, gravity and the delta-v requirement.
Io
DIFFICULTY: HARD
Io's gravity is strong and is close to Jupiter, making orbits near or at its orbit have a high velocity. Getting to orbit may require lots of fuel. So it is advised to intersect Io's orbit, then do the transfer burn.
Europa
DIFFICULTY: EASY
Europa's small gravity, small size and its proximity to Jupiter makes it relatively easy to get to orbit on it. The amount of fuel can be relatively low.
Ganymede; Callisto
DIFFICULTY: MEDIUM
Ganymede and Callisto are both far away from Jupiter. But getting to orbit on Ganymede is much harder than in Callisto because of its high gravity. Now let's upgrade Ganymede's difficulty to HARD.
Atmospheric entry[]
Atmospheric entry on different planets depend on atmospheric pressure and velocity.
Venus[]
DIFFICULTY: HARD
Venus's thick atmosphere can destroy any rocket passing through its atmosphere at a high velocity, even with a heat shield.
It is recommended to get to orbit on Venus before landing because of its low velocity.
Earth[]
DIFFICULTY: MEDIUM
Earth is usually the landing site for rockets that came from other destinations. Usually, a rocket reentering the atmosphere with a high velocity may or might be destroyed; but with a low velocity, it will usually survive the heats of reentry.
Mars[]
DIFFICULTY: EASY
Mars's tenuous atmosphere can result in easier atmospheric entry. Rockets that travel from Earth tend to be not be destroyed even with a high velocity.
Deorbiting directly from Mars can result in an entry having low temperatures around 1300 to 1900°C. Heating effects still happen even at lower altitudes.
Jupiter[]
DIFFICULTY: HARD
Because of its dense atmosphere and its size, a rocket passing through the atmosphere of Jupiter won't survive below 80 kilometers. It is recommended to use the No Heat Damage cheat to survive atmospheric entry on Jupiter.
Landing[]
Mercury[]
DIFFICULTY: MEDIUM
Mercury is often called the graveyard because of the difficulty of getting there.
Landing on Mercury can be a little hard because of the sometimes rough terrain. It is recommended to land on Borealis Planitia because of its flatness.
Venus[]
DIFFICULTY: MEDIUM
Landing on Venus is also a little hard because of its thick atmosphere and rough terrain. A strong heat shield or a low landing velocity is a must for a landing on Venus. When near the surface, deploy a parachute or two (if your rocket is heavy) to slow down the touchdown speed. It is required to keep your heat shield on Venus because of its high temperature.
Earth[]
DIFFICULTY: EASY
Earth is the landing place for returning rockets from other celestial bodies. When nearing the atmosphere at a high velocity, slow down to survive reentry. When at the lower layers of the atmosphere use parachutes to slow down the landing. Landing legs or a landing burn may be needed if the landing speed is too fast.
Moon[]
DIFFICULTY: EASY
Because the moon is the closest celestial body to Earth, it is easy to explore. Landing missions are common on the moon.
When you deorbit, use your engines to slow down the descent to the surface. Try to land on a flat spot with no or few terrain irregularities and slow down the velocity to >5 m/s for a soft touchdown.
Mars[]
DIFFICULTY: EASY
Landing on Mars is easy as landing on the Moon although with a few challenges. Try to descend to a low velocity before landing to avoid heating effects. When the rocket's altitude drops below 4 kilometers, deploy the parachutes. Landing legs are necessary. A landing burn before touchdown may be needed.
Because of the low atmospheric pressure of Mars, parachutes don't work properly as on Earth; so, multiple parachutes is a must.
Mars's moons[]
DIFFICULTY: EASY
Mars's moons have low gravity so it is easy to land on them because of the low velocity needed to land.
Galilean moons[]
Io is difficult to land on because of its proximity to Jupiter and its high gravity. Add it with rough terrain and it will be even harder.
Europa is the easiest moon of Jupiter to explore. It has a low gravity and smooth surface, smoother than any celestial body. Landing on it requires the same amount of fuel as landing on the moon, if you start from orbit.
Ganymede is the hardest Galilean moon to explore. The high gravity and rough terrain makes it difficult to land on it.
Callisto is another moon of Jupiter that is easy to explore, but it is harder than Europa. The cratered surface is relatively smooth. Its gravity is lower than Io, making it easy to land on.
Recap time![]
These are the final results of the difficulty of getting to different celestial bodies.
Sun[]
Visiting the sun is easy because it's the star orbiting Earth. Here one can deploy multiple satellites to orbit the sun. They can also escape the solar system to explore the interstellar void.
A rocket passing very close to the sun will melt.
Mercury[]
DIFFICULTY: HARD
Mercury is the hardest planet to explore because of its proximity to the sun. A rocket must need a couple of gravity assists from other planets and itself to get to it safely.
Venus[]
DIFFICULTY: MEDIUM
Venus may seem to be easy to land on, but its atmosphere can be deadly sometimes. A landing on Venus can be quite easy, but you must wait for a couple of minutes before nearing the surface.
Earth[]
DIFFICULTY: EASY
Earth is both the starting point and ending point for most rockets. A landing on Earth can be nailed by parachutes or a landing burn.
Moon[]
DIFFICULTY: EASY
The moon is easy to explore because it is the satellite of Earth. Many activities can be also done there.
Mars[]
DIFFICULTY: EASY
Mars is easy to explore — although it is farther away from the moon. Its atmosphere is thin so it can be sometimes ignored.
Phobos[]
DIFFICULTY: EASY
Phobos is a moon of Mars. It is easy to land on it because of the low gravity.
Deimos[]
DIFFICULTY: EASY
Like Phobos, Deimos is a moon of Mars and very easy to explore. Its lack of gravity can make landings easy.
Jupiter[]
DIFFICULTY: EASY
Although it has some difficulties exploring it, Jupiter is relatively easy to explore. You can do a lot of activities there.
Galilean moons[]
DIFFICULTY: Depends
The Galilean moons have their own terrain and landing difficulty, so it is interesting to explore them.
Conclusion[]
Celestial bodies have their own difficulty to get there, like orbiting or landing on them. If it's hard to get there, you must make some techniques to get to that celestial body.