# Why not a landing platform with solar cells on the Mars 2020 rover for the helicopter scout?

In May 2018 the Mars Helicopter Scout (MHS) was approved to fly on the Mars 2020 mission.

Author: NASA/JPL-Caltec.

It's a solar powered helicopter drone with a mass of 1.8 kg and a coaxial rotor diameter of 1.2 m.

In this recent publication about the design and development of the helicopter:

The helicopter is powered by a Li-Ion battery system that is recharged daily by a solar panel. The energy in the battery is used for operating heaters to survive the cold Martian nights as well as operate the helicopter actuators and avionics during short flights lasting from 90 seconds to a few minutes. Depending on the latitude of operations and the Martian season, recharging of this battery through the solar panel could occur over one to multiple sols (Martian days).

The on board solar panel has a 544 cm$^2$ active cell area and is centered above the co-axial rotors.

It is estimated that with an available battery capacity of about 36 Wh, night-time survival energy usage will be 21 Wh and approximately 10 Wh is available for flight.

Could not the duration and the frequency of the daily flights of the helicopter be enhanced considerably by recharging the battery with solar cells on a telescopic landing platform placed on the rear end of the Mars 2020 rover ?

With a platform of 2 x 2 meters, a landing would not be that difficult for a helicopter with a coaxial rotor diameter of 1.2 meters, even with a simple demonstration model like this one.

With a surface area of 40,000 cm$^2$ for instance, recharging the helicopter's battery could be easily done more than 4 times a day on this platform, while at night the scout could remain on the platform to be kept warm with the rover's onboard energy.
So in contrast with a stand alone helicopter, with the platform the scout can use all the available battery capacity for flight and at once.

Furthermore several flights in different directions could be done within one day, speeding up the exploring capacity considerably.

And it will be advantageous to have much more energy for the rover and its instruments as well.

• A landing platform with solar cells would limit the helicopter to a very small area because it must return to the platform after each flight. If the platform is missed one time there is no other chance. – Uwe Jul 21 '18 at 13:39
• @Uwe You're right, so the helicopter has to keep it's own solar panel in case of emergency. – Conelisinspace Jul 21 '18 at 13:55
• @Uwe Without a platform the helicopter would be limited to a daily flight of 90 sec. and a flight range up to 300 m., because much energy is needed to keep it sufficient warm at night. With the platform almost all the energy of the on board battery can be used for flight and because of that the flight range could be up to 900 m. That would not be a small area. – Conelisinspace Jul 21 '18 at 17:17
• Why not a blimp drone – anon Jul 23 '18 at 11:58
• @anon I don't know, could be a good question, maybe with some interesting answers. – Conelisinspace Jul 23 '18 at 22:22

Mars Helicopter Scout is "just" a demonstration mission to show that it is possible to operate an airborne vehicle on Mars. It has very limited capabilities, such as the total weight of only 1.8 kg.

• the helicopter is just an additional feature, but nothing like an integral part of the mission. Slamming 2 kg of material on top of a rover with delicate measurement devices is not a perfectly safe thing to do. Hence, the helicopter is planned to only operate at a safe distance to the rover.

• if you land on top, you need means to fasten the helicopter as well. Imagine the rover climbing up a slope, the helicopter with empty batteries on top slides down and one of its legs gets stuck in a wheel.

• it's likely there is no more advanced sensors on board than an accelerometer and cameras. For a precision landing on top of another structure you would need a lot of real-time image processing and guidance.

• the helicopter is built to not do soft landings but for being dropped from an effective height of up to 1.1 meter (0.3 m plus 2.5 m/s velocity, see Mars Helicopter Technology Demonstrator)

• the platform of 4 m² as proposed in the edited question would add a lot of complexity to the whole project. Typical panels used on satellites weigh about 2 kg per square meter, not counting for the additional reinforcement needed on Mars and to support the helicopter on the them. On top comes the necessary electronics and mechanics to deploy the panel. I'd assume a total weight of at least 15 kg, 8 times more than the current design.

I think that it's very likely that a future extended helicopter mission to Mars will use a scheme like you proposed, but this small-scale demonstration mission is just too early.

• as well as landing there would need to be some way of passing charge from the rover; a mechanical connection would have to be sand proof and probably require an increase the landing precision. Wireless power runs into risks of interfering with the rover systems. Having to return to the rover limits the drone range to less than half it's flight time, vastly undermining it's utility as a scout for the rover route planners. – JCRM Jul 21 '18 at 10:30
• @JCRM Could not wireless power transmission be shielded enough ? A stand alone helicopter can only use one third of the battery's energy, so has a daily flight time that is less than the half flight time with the platform. And those flights could be done easily 4 times a day in several directions from the rover ! – Conelisinspace Jul 21 '18 at 11:16
• Thank you for your answer. I agree with you that real-time image processing and guidance will be needed, but of course, the helicopter doesn't have to be on the platform when it's travelling, so no slamming on delicate devices will happen because of that. – Conelisinspace Jul 21 '18 at 11:34
• Of course the platform is there to protect the delicate devices and with a gravity on Mars less than half that on Earth, i would say "slamming material " are not quite the right terms to use – Conelisinspace Jul 21 '18 at 11:54
• @Conelisinspace It corresponds to dropping 2 kg from 40 cm height on Earth onto a rigid surface. And this is only the design value, not the impact in case of a malfunction! If you want to put the helicopter aside while moving, this will cost you at lot of flexibility (no rover driving while the battery of the copter is empty) and the limited flight distance also limits the driving capability. – asdfex Jul 21 '18 at 12:51