NASA’s ambitious plan to fly a robotic vehicle on a moon of another world is to go ahead after receiving official confirmation in April 2024. With its cost now set at some US $3.35 billion, double its initial price estimates – largely the result of the COVID pandemic derailing the vehicle development process in 2020/21 -, the vehicle – called Dragonfly (as is the overall mission) is intended to have a 10-year primary lifespan, with 3.3 years of that time spent flying around and studying Saturn’s largest moon, Titan.
Dragonfly is a spectacular science mission with broad community interest, and we are excited to take the next steps on this mission. Exploring Titan will push the boundaries of what we can do with rotorcraft outside of Earth.
– Nicky Fox, NASA associate administrator, Science Mission Directorate, Washington D.C.
Titan is a unique target for extended study for a number of reasons. Most notably, and as confirmed by ESA’s Huygens lander and NASA’s Cassini mission, it has an abundant, complex, and diverse carbon-rich chemistry, while its surface includes liquid hydrocarbon lakes and “seas”, together with (admittedly transient) liquid water and water ice, and likely has an interior liquid water ocean. All of this means it is an ideal focus for astrobiology and origin of life studies – the lakes of water / hydrocarbons potentially forming a prebiotic primordial soup similar to that which may have helped kick-start life here on Earth.
Using a vehicle that is in situ on the surface of Titan is vital, because the moon’s dense atmosphere obscures its surface across many wavelengths, making it exceptionally hard to definitively identify the specific combinations of hydrocarbon materials present across the moon’s surface without getting very up close and personal. To do this, Dragonfly will be a unique rotary vehicle, one a good deal heavier and more complex / capable than the Ingenuity drone flown on Mars (which was an extraordinary flying vehicle – and now static weather station – on Mars).
The brainchild of Jason W. Barnes (University of Idaho) and Ralph Lorenz (Johns Hopkins University Applied Physics Laboratory – or JHU/APL), Dragonfly is being developed for NASA by JHU/APL, with Elizabeth “Zibi” Turtle, a planetary scientist at JHU /APL serving as the mission’s principal investigator.
The craft is designed as an octocopter – an aerial vehicle with four pairs of contra-rotating rotor blades. Each pair of rotors will be powered by its own electric motor, and the craft has been design to withstand either the loss of a single rotor blade or the completely failure of and one motor powering a pair of blades. It will have an on-the-ground mass of around 450 kg (compared to Ingenuity’s 1.8 kg), and will use a mix of nuclear and battery power.
A large lithium-ion battery will provide direct power to the vehicles flight and navigation systems and to this science suite. It will provide sufficient power for the craft to travel up to 16 km on a single charge at speeds of up to 36 km/h, with a maximum airborne time of around 30 minutes per flight, and an estimated maximum altitude of 4 km – although generally the craft will fly much lower than this. The battery will be supported / recharged by a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), which will also be used to provide heat to the vehicle, particularly during Titan’s night periods when it is behind Saturn relative to the Sun, and which lasts for 8 terrestrial days. The MMRTG will additionally provide power to the vehicle’s science instruments during the night periods, allowing them to work whilst the vehicle waits out the night in order to resume flying in daylight..
Dragonfly’s remarkable flight capabilities – speed, altitude, single flight distance – are made possible by Titan’s environment: the moon’s low gravity (around 13.8% that of Earth and dense atmosphere (around 1.45 times that of Earth’s) mean that the flight power for a given mass operating on Titan is around 40 times lower than on Earth, so the vehicle can have a fairly significant mass which can be lifted by relatively low-mass, low-power motors.
A Dragonfly testbed article undergoing flight trials
The vehicle will fly a primary science suite of four packages, comprising:
- DraGNS (Dragonfly Gamma-Ray and NeutronSpectrometer): comprising a deuterium-tritium Pulsed Neutron Generator and a pairing of a gamma-ray spectrometer and neutron spectrometer to identify the surface composition under the vehicle.
- DraGMet (Dragonfly Geophysicsand Meteorology Package): a suite of meteorological sensors including a seismometer.
- DraMS (Dragonfly Mass Spectrometer): a mass spectrometer to identify chemical components, especially those relevant to biological processes, in surface and atmospheric samples.
- DragonCam (Dragonfly Camera Suite) is a set of microscopic and panoramic cameras to image Titan’s terrain and scout for scientifically interesting landing sites.
Samples of surface material for examination by the science packages will be obtained using two coring drills and hoses mounted within Dragonfly’s skid, per the video below.
Further, the vehicle will be equipped with a fully autonomous flight and navigation system capable of flying it along a selected flight path, making its own adjustments to account for local conditions whilst in flight, and with sensors capable of record potential points of scientific interest along or to either side of its flight path, so the information can be relayed to Earth and factored into planning for future excursions. Flights over new terrain will likely be of an “out and back” scouting nature, the craft returning to its point of origin, allowing controllers on Earth to plan follow-up flights to locations along the flight track, taking into account any points of interest noted by the vehicle.
Currently, Dragonfly is targeting a July 2028 launch, although the launch vehicle itself has yet to be announced. It will take seven years to reach Titan, mostly likely using several gravity-assist manoeuvres around Earth to slingshot itself on its way. In this, it will be the first dedicated mission to the outer solar system not to flyby / utilise Jupiter whilst en route, as the planet will not be within the mission flight path.
On arrival at Titan, and following separation from the cruise stage that would keep it both powered and warm during the trip from Earth, Dragonfly will enter the moon’s atmosphere atop a 3.7 metre diameter heat shield, and under a protective back shell. Once in the atmosphere, a single drogue and single large main parachute will be deployed to slow the vehicle’s descent until it reaches an altitude at which the parachute is released and Dragonfly can drop clear of the back shell, enabling it to start its motors and make a first landing on Titan.
In this, the landing site for the mission has already been selected: the edge of a prominent and dark region of Titan called Shangri-La, thought to be an immense sand sea of dark, carbon-rich material.
Specifically, Dragonfly will touch down in a dune field close to the relatively young Selk impact crater, which will be the vehicles first science study location, as it contains strong indications that it was once home to deposits of liquid water (and is now surrounded by ejecta that includes water ice) and contains tholin organic compounds. After this, Dragonfly will move on into the Shangri-La, carrying out exploratory flights of up to 8 km at a time and gathering samples for analysis from diverse locations.
NASA Re-Re-Rethinks Mars Sample Return Mission
NASA is now officially seeking both internal outside support for its much-troubled Mars Sample Return (MSR) mission.
The goal of returning samples of surface and sub-surface material from Mars to Earth, where it can be subjected to much more intensive and multi-disciplinary study than can be achieved via in-situ robotic explorations, has long be sought. For NASA, the last 20 years have seen numerous ideas put forward for gathering and returning such samples from Mars, all of which have ended up being cut down in their prime due to matters of cost and stringent curbs on the US space agency’s budget – sending a vehicle to Mars with the express intent of obtaining, storing and then returning samples to Earth not being the easiest of mission profiles to plan, let alone achieve.
However, in the lead-up to the Mars 2020 mission, featuring the rover Perseverance, NASA and the European Space Agency (ESA) signed a letter of intent to jointly develop a sample return mission based around the concept of the actual sample gathering being carried out by Perseverance and deposited on the surface of Mars for collection “at a future date”. The operation to start depositing groups of these samples actually started on December 21st, 2022, with a total of 10 sample tubes being deposited relatively close together on Mars by Perseverance.
Whilst this approach negated the need for the MSR to actually collect and store samples itself – in theory simplifying the mission parameters – actually settling on a final design for the mission proved difficult. By 2021, the “optimal” approach was seen as being a mission involving four unique vehicles in addition to the Mars 2020 rover. These were:
- A NASA- built Mars lander / launch platform.
- A NASA-built Mars Ascent Vehicle (MAV) with a specialised sample containment unit, and carried within the lander.
- A European-built “fetch” rover with its own dedicated lander, designed to land ahead of the NASA lander and go find the sample tubes deposited by Perseverance, bring them to the NASA lander and transfer them into the sample containment unit in the MAV.
- A European-built Earth Return Vehicle (ERV) designed to arrive in Mars orbit and await the arrival of the NASA-built MAV from the surface of Mars. This would then capture the sample unit (about the size of the basketball) after the latter had been released by the MAV, secure it and the samples inside itself and then make the return trip to Earth.
So, yeah; “simples” – not. The mission included, as identified by independent review board (IRB) charged with reviewing the mission for its overall cost-effectiveness and feasibility, no fewer than eight “break the chain” (and cause the mission to fail) first-time challenges, including the fully robotic collection and transfer of samples, the first automated launch of a vehicle from the surface of another planetary body, the first fully autonomous orbital rendezvous between two vehicles (the MAV and the ERV), and the first “pitch and catch” transfer of a sample package. However, despite this and concerns over the estimated mission cost rising to around US $4 billion, the IRB green lit the mission.
The MSR mission concept as envisioned in 2021 / early 2022 and featuring the ESA-built “fetch” rover (minus its lander). Credit: NASA / ESA
By July 2022, the complexities of the mission had been more fully realised, so efforts were made to “simplify” it. Specifically, the ESA “fetch” rover was eliminated from the mission – but was supplanted by the use of two Ingenuity class Mars helicopters. Fitted with wheels, these would also be delivered to Mars by the NASA lander carrying the MAV, and once there, they would fly and land in close proximity to sample tubes deposited by Perseverance, then drive up to them, pick them up and fly them back to the lander for transfer to the MAV, with the rest of the mission remaining the same.
However, while this removed the need for an entire rover and lander, and meant that effectively, NASA would have two further helicopters on Mars with which they could carrying out other missions once the sample tubes had been delivered to the MAV, it didn’t actually do much to reduce complexity or mission cost – which threatened to rise to around US $8 billion.
To offset this, the planned mission time frame was revised from around 2030-31 to the mid-to-late 2030s, allowing the mission cost to be spread across a greater number of NASA fiscal years. However, by mid-2023, it was widely recognised that the mission would probably exceed the US $8 billion estimate and peak at perhaps as much as US $11 billion – gaining the mission a lot of opposition on Capitol Hill. Suggestions were made to push the mission time-fame out further, with the lander / MAV / helicopter element not launching until the early 2040s.
By mid-2023, the mission had been further revised in order to try to reduce complexity and costs. Under the new proposal, none of the sample tubes thus far used and deposited on Mars for collection by Perseverance would actually be recovered (about 24 of the 43 total). Instead, all of the remaining tubes (16 of which have yet to be used, as of the time of writing) would be retained on the rover. Then, on the arrival of the MSR lander / MAV combination, Perseverance would rendezvous with them and load its supply of sample tubes directly into the MAV’s sample capsule for onward transfer to the ERV and a return to Earth. Whilst this would limit the selection of samples compared to gathering them from the various caches the rover had made on the surface of Mars, it did both simplify the mission – NASA only having to fly the MAV-carrying lander – whilst ensuring ESA’s involvement was not wasted, as they would still supply the Earth Return Vehicle.
The 2023 MSR update, with Ingenuity class helicopters removed and showing the Perseverance rover directly transferring sample tube to the sample capsule of the MAV, eliminating the need for intermediary vehicles. Credit: NASA / ESA
Despite this, over mission complexities and the need for the development of two entirely new classes of robotic spacecraft (the MSR lander-come-launcher for the MAV, and the MAV itself, complete with its sample storage / containment system) meant NASA would still be looking at around a minimum US $8 billion cost – and if the timeframe for the mission were to be extended into the early 2040s, inflation would likely push the final price back up towards the US $11 billion figure.
As a result, and with NASA’s budget already being severely stressed for the 2024/25 period, the agency finally admitted defeat with its more grandiose MSR plans, and on April 15th, 2024, the US space agency issued a statement indicating it is now looking “outside the box” for the means to carry out a Mars sample return mission in a cost-effective manner and within a reasonable time-frame (i.e. before the end of the 2030s). To this end, the statement calls on all NASA centres involved in Mars exploration to work together in order to develop such a mission, whilst also indicating the agency will seek proposals for potential mission architecture from the private sector.
Currently, NASA itself has admitted it does not have firm ideas on how mission costs can be reduced, but is determined to see the sample return mission take place, viewing it as a vital precursor to any attempt at a human mission to Mars. Thus, the process for redeveloping plans and ideas is expected to run through until the latter part of autumn 2024.
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