Difference between revisions of "Tutorial:How to get to Duna"

Latest revision as of 01:23, 15 September 2022

Duna. If you don't see this at some point during the tutorial, you've probably done it incorrectly.

Traveling to Duna

Duna is Kerbin's second closest neighbor. It is likely your next logical step after landing on the Mun, Minmus, or Eve. It is perhaps the ideal planet for interplanetary voyages for several reasons:

1. Its close proximity to Kerbin.
2. Its low orbital eccentricity.
3. Its small size and gravity well (comparable to The Mun).
4. Its atmospheric composition is thick enough to support aerobraking, yet also thin enough to permit an uncostly ascent back to orbit.
5. Possessing a moon similar to Kerbin's, Ike, in addition to several mysterious Easter Egg locations.

With a little bit of luck, skill, and determination, you can successfully land on Duna and return to Kerbin, all in one ship, with ease.

Specifications

• Length: 1–3 hours
• Difficulty: Moderate/Hard
• For version: .17
• Recommended Delta-V: ~7760 m/s (8960 m/s without aerobraking)
  • ~4700 m/s to orbit around Kerbin
  • ~1060 m/s for interplanetary transfer
  • ~1500 m/s for ascent to orbit.
  • ~500 m/s for return to Kerbin (1700 m/s without aerobraking)

Additionally, you will need a good understanding of orbital mechanics (see Tutorials section), angles, and a lot of patience.

Steps

Step 1 - Build Your Rocket

An extremely barebones, lightweight interplanetary rocket. Despite having no middle stage it can reach Duna, and return to Kerbin with a little piloting skill.

To perform a successful landing on Duna you will need a large rocket. Unless you are planning to deploy a spaceplane in the Dunan atmosphere (a perfectly viable option), you will need something resembling a highly beefed-up Mun Rocket.

Upper Stage

Balancing this stage is tricky. Largely similar to a Mun lander, with several key differences:

1. With proper parachute rigging, it will require little/no thrust for a landing. Note that unless your ship is a probe, there is no need to store extra parachutes for Kerbin as long as you bring an engineer to repack them.
2. For a return to Kerbin, you MUST touch down with at least 1 large fuel tank and an engine with high specific impulse intact.

The best way to describe something that can get off of Duna, is a ship somewhere between one that can take off from the Mun, and one that can take off from Kerbin. You will need at least 2000ms Delta-V for the orbit and return, you can test this by seeing if your lander is **almost** capable of reaching Kerbin orbit by itself.

Middle Stage

This is the stage that will be doing a lot of the work. It must be capable of getting from Kerbin to Duna, and positioning your lander craft for the terminal descent. It must carry enough fuel for the DeltaV you will need to successfully pull this off.

Lower Stage

This stage should take you at least into Kerbin's orbit if you hope to reach Duna. It will require several large thrusters to lift the interplanetary vehicle itself into orbit, probably assisted by some SRBs. For reference, it should be about 1.5x bigger than what you would need for a 1 way trip to Eve.

Step 2 - Planetary Alignment

While not absolutely essential, the easiest and fastest way to reach Duna from Kerbin is ensuring that they are properly aligned. Otherwise, you may spend a lot of time (possibly years) and fuel drifting until they happen to match up.

To do so, check your map and make sure that Duna is ahead of Kerbin in its orbit around Kerbol.

Look at it like a clock. If Kerbin is at 3 o'clock relative to the Sun, Duna should be at 1:30. Warp until they are in this position relative to each other.

If you look at it in degrees, with Kerbin at 3:00 relative to the sun, Duna should be ~45 degrees ahead of Kerbin.

Alternatively, you can visit The Interplanetary Guide and Calculator to calculate your own path.

Step 3 - Launch to Kerbin Orbit

Take off as usual (see Tutorials for how to achieve orbit), heading east for a counter-clockwise (CCW) prograde orbit. Unless you've done your own calculations, try to aim for a circular equatorial orbit at around 120,000 meters.

Step 4 - Fly from Kerbin to Duna

When you reached your desired orbit around Kerbin, begin your high-velocity burn. Keep an eye on your map, wait until you are at about 5 o'clock around Kerbin (150 degrees), and get your velocity up to approximately 3020 m/s.

It's really important to watch the map while you are accelerating. As you accelerate your Kerbolar orbital path should move to intersect Duna's. If all goes well, there should be a brief moment where you are captured by Duna's gravity well right around the target velocity. Immediately cut your thrust. If you overshoot, just turn the craft around and do a slight retro burn until you are caught again (or just do it with RCS).

This journey should take 70–120 days. While you are traveling around Kerbol, consider tweaking your trajectory until your periapsis around Duna is at the equator, and lower than 100 km.

Step 5 - Arriving at Duna

When you enter Duna's sphere of influence you will always be traveling at escape velocity. If you have fuel to spare, simply burn retrograde at periapsis to achieve some kind of orbit.

You can reduce the amount of fuel required to enter orbit around Duna by aerobraking. As shown on the information page, Duna's atmosphere is thin and only begins around 40 km. Aerobraking from escape velocity requires you to place your periapsis at 15 km or less, which can be quite a rush given your surface speed is likely 2 km/s or more. If your periapsis is too high you will need to burn retrograde after the aerobrake to achieve an orbit. Duna's highest terrain is around 8500m high, so placing your periapsis below that is not recommended even for the bravest. A heat shield might be necessary, but a good aerodynamic vehicle won't need it.

Note that if your resulting orbit's apoapsis is far enough out Ike can get in the way as it has the biggest sphere of influence compared to its planet. This can be useful, as experienced players can use a gravity assist to enter a Dunan orbit.

You can lower your orbit with aerobraking by placing your periapsis slightly under 40 km. Putting your periapsis under 10,000 meters will likely result in a landing. If you are not planning on landing, once your apoapsis is at your desired altitude, burn prograde at apoapsis to raise your periapsis above the atmosphere and circularize your orbit.

Step 6 - Land on Duna

Continue aerobraking to bleed off extra velocity and lower your orbit, or use orbital burns to achieve a low orbit. Then pick a landing spot and burn retrograde until your orbital path hits the planet slightly after your desired landing spot (since Duna's atmosphere will slow you a bit). Note that Duna's atmosphere is thinner and smaller than Kerbin's, and so is your margin of error. Deploy your chutes around the 5k mark, and lower whatever landing gear you brought with you. Duna's thin atmosphere means chutes aren't nearly as effective as they are on Kerbin so you may need to fire retro rockets to slow your descent unless you packed a lot of chutes. Ultimately we're going for typical touchdown speed (6–12 m/s). Duna has uneven terrain and much higher gravity than the Mun, so be careful to avoid tipping over on landing, unless you plan on staying.

Congratulations! You've landed on another planet! Walk around, feel the freezing, toxic breeze of an afternoon on Duna!

Before you head off home, make sure to repack your parachutes for landing on Kerbin. To do this, EVA a kerbal, right click a parachute and click 'repack chute' (The kerbal must be at least a level one engineer to do this). The chute should revert to its state before it was deployed. Get back into your rocket, put your newly packed chute into the correct stage, and go to the next step of the tutorial.

Step 7 - Back to Orbit

Make sure Duna and Kerbin are in the proper alignment. This time, Duna should be at 3 o'clock with respect to Kerbol, and Kerbin itself should be at roughly 5:30. Warp until they are in alignment, do not take off until this has been achieved.

While not nearly as difficult as ascending from Kerbin, you are still negotiating a decent-sized gravity well and an atmosphere. Our goal is to conserve as much fuel for the interplanetary burn as possible. Try to aim for a circular orbit, roughly 70 km altitude, around Duna's equator.

Step 8 - Fly from Duna to Kerbin

Thankfully, this step requires less than half as much Delta-V as the trip from Kerbin to Duna. When Duna's orbit is at 10 o'clock relative to Kerbin (-75 degrees), begin your burn. Our final velocity is going to be somewhere around 1500 m/s.

When you are captured by Kerbin, tweak your approach as much as you can in advance, we're running on a tight fuel budget here and the sooner you make adjustments the less fuel you will need. If you can get your periapsis within 50 km of Kerbin, you will not need to burn for the rest of the trip.

Step 9 - Landing back on Kerbin

Once you are back in Kerbin's SOI, make whatever changes to your approach you want to assuming you still have fuel. Keep your periapsis somewhere below 50 km, keep it shallow though for a safe descent.

Jettison your lander stage and go in with just the command module. Hopefully you've repacked your parachute(s) by now. If not, you better hurry up and repack them!

Congratulations! Once you've succeeded at a round trip to Duna, anything is possible.

Ideas

Land on Duna's moon, Ike

Hunt for the various easter eggs on Duna's surface.

Attempt a round trip to Eve (extremely difficult, but not impossible).

Fly to the next furthest body from Duna, the dwarf planet Dres.

Using a rover mod or the Probodobodyne RoveMate stock part, reattempt the Mars rover "Curiosity" landing!