Can we adapt the Antarctica IceCube Neutrino Observatory drilling technique to explore the subice oceans of Europa?

 Copyright 2023 Robert Clark

 The IceCube Neutrino Observatory was able to drill down 2.5 kilometers rapidly into the ice in Antarctica using a relativly simple method using heated, pressurized water. Can we adapt this to reach the subice oceans on Europa?

 Here is a published description of the drilling method:

IceCube Enhanced Hot Water Drill functional description.
Published online by Cambridge University Press:  26 July 2017
T. Benson, J. Cherwinka, M. D
https://www.cambridge.org/core/journals/annals-of-glaciology/article/icecube-enhanced-hot-water-drill-functional-description/F2A93B250A9FDB4E8A94101787BA3A68

 The specifications:

 The total power for drilling a 60 cm wide hole was 5 MW. The great majority of this was the thermal power of 4.7 MW for melting the ice. 

 For just sending a small probe beneath the ice we'll make the hole width smaller by a factor of 10 to 6 cm, 2.4 inches. A probe of greater capabilities will be obtained by simply making it longer, while keeping it the same width.

 The required power will scale by the cross-sectional area to 50,000 watts, 50 kW. 

 In this blog post I noted the Falcon Heavy can send a 1 ton spacecraft to the surface of Europa using currently existing in-space stages:

Low Cost Europa Lander Missions.
https://exoscientist.blogspot.com/2015/02/low-cost-europa-lander-missions.html

 The Europa Clipper mission currently planned for launch in 2024 on the Falcon Heavy is an orbiter mission though; it will not have a lander. However, the cost of the Falcon Heavy is only ca. $100 million, so a second launcher for the lander mission can easily be purchased. By the way, an interesting and much appreciated phenomenon I've observed about NASA science missions is the time between announcement and actual mission launch seems to much more rapid than before. So it's likely the lander mission can be launched also within the ca. 2024 time frame.

 There have been several proposals to drill through the Europan ice. But they frequently suggest doing it over long time frames, several months. For instance, the proposal discussed at about the 8:50 point in this video would take up to a year:

 The IceCube drill though took only 30 hours to go through 2.5 kilometers of ice in Antarctica. For a 15 kilometer thick ice shell on Europa that would be about 7.5 days. However, because of the fractured surface of Europa the ice shell is believed to be much thinner in some place, perhaps as low as 5 km thick. In that case, the drill may only take 2.5 days to penetrate the ice.

 The REASON ice-penetrating radar on the Europa Clipper orbiter can be used to first determine thinnest locations on the ice for the lander to land at.

Supplying the Energy.

 But first how to get 50 kW power at Europa? We have a limit of about 1 ton for the lander spacecraft payload to be launched with in-space stages on the Falcon Heavy. First, space fission reactors. Here's a list of space fission reactors that have flown in space:

Name and model	Used on (# of RTGs per user)	Maximum output		Radio- isotope	Max fuel used (kg)	Mass (kg)	Power/mass (Electrical W/kg)
		Electrical (W)	Heat (W)
MMRTG	MSL/Curiosity rover and Perseverance/Mars 2020 rover	c. 110	c. 2000	238Pu	c. 4	<45	2.4
GPHS-RTG	Cassini (3), New Horizons (1), Galileo (2), Ulysses (1)	300	4400	238Pu	7.8	55.9–57.8[48]	5.2–5.4
MHW-RTG	LES-8/9, Voyager 1 (3), Voyager 2 (3)	160[48]	2400[49]	238Pu	c. 4.5	37.7[48]	4.2
SNAP-3B	Transit-4A (1)	2.7[48]	52.5	238Pu	?	2.1[48]	1.3
SNAP-9A	Transit 5BN1/2 (1)	25[48]	525[49]	238Pu	c. 1	12.3[48]	2.0
SNAP-19	Nimbus-3 (2), Pioneer 10 (4), Pioneer 11 (4)	40.3[48]	525	238Pu	c. 1	13.6[48]	2.9
modified SNAP-19	Viking 1 (2), Viking 2 (2)	42.7[48]	525	238Pu	c. 1	15.2[48]	2.8
SNAP-27	Apollo 12–17 ALSEP (1)	73	1,480	238Pu[50]	3.8	20	3.65
(fission reactor) Buk (BES-5)**	US-As (1)	3000	100,000	highly enriched 235U	30	1000	3.0
(fission reactor) SNAP-10A***	SNAP-10A (1)	600[51]	30,000	highly enriched 235U		431	1.4
ASRG****	prototype design (not launched), Discovery Program	c. 140 (2x70)	c. 500	238Pu	1	34	4.1

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Nuclear_power_systems_in_space

 Note to get to 50 kW would require several hundred kg just for the power system alone, leaving little for the rest of the spacecraft operations. One might also not like to leave radioisotopes on a world that may have life.

 Solar power? Normally the high power requirements would make this a non-starter for the far away Jupiter system with its reduced solar insolation. But quite key here is the majority of the power needs to be thermal. The inefficiencies of space solar power come from when it has to be converted to electrical power. Jupiter gets about 50 watts per square meter of solar power, well less than the 1,200 W per square meter at Earth. Then you would need 1,000 square meters solar collecting area, about 32m x 32m. But you would not send this to solar electric cells. You would collect it either by a parabolic mirror or Fresnel lens to concentrate it to achieve a temperature of up to 3,000°C. In the low gravity of Europa this would need minimal support structures and might weigh only a few tens of kilos total weight. For instance the Sunjammer solar sail only weighed 32 kg at a 1,200 square meter area. 

 Burning fuel? The disadvantage here is that higher fuel load would need to be carried to Europa for a longer time the drill had to be run. To estimate the power using a rocket engine to deliver the thermal power. it's at 1/2 times the square of the exhaust velocity per fuel flow rate. Or equivalently, the amount of energy per kilogram propellant is 1/2 times the square of the exhaust velocity. Given a (very) large expansion ratio the exhaust velocity of a hydrolox engine can be ca. 4,800 m/s. So the energy per kilo of propellant would be 11.5E6 J/kg. If we ran our 50 kW thermal power system for 7.5 days for a 15 km thick ice shell, it would take 50,000*7.5*24*3,600 = 32.4E9. This would take 2,800 kg of propellant, far too much.

Estimates of power requirement for Europa. 

 The above was assuming the IceCube drilling method could be adapted to Europa, specifically the energy requirements. This page actually does the calculation from first principles for Europa:

Calculating the Required Energy of Drilling into Europa.

July 9, 2020 by Engineer Calcs

https://engineercalcs.com/calculating-the-required-energy-of-drilling-into-europa/

 It discusses three methods: 1.)breaking up the ice and simply carrying the broken up ice to the surface, 2.)bringing the  -160°C ice on Europa only up to a easier to achieve sublimation temperature of -75°C rather than to the melting point of 0°C, and allowing the ice to sublimate to a gas in the vacuum of Europas surface, and 3.)bringing the ice up to the 0°C melting point and using analogous methods as to the IceCube experiment.

 The first method requires surprisingly low amounts of energy. For his calculation, the author takes the width as 1-meter and the depth 25 kilometers. The enegy requirement is simply calculated by the potential energy of raising that much mass of ice the required height in the low gravity of Europa. He calculates 5.92E11 Joules. However, our case will be smaller in using only a 6 cm wide drill hole and assuming at most 15 km height. Also, in actuality not the entire column needs to be raised the full height. The ice near the top for example needs to be raised hardly at all. The height and the energy needed to raise is a linear function of the depth of that portion of the ice. Then the energy can be calculated by using just the middle point of the height, i.e., only 7.5 km for our 15 km drill hole. Then the energy is:

5.92E11*(6/100)^2*(7.5/25) = 6.4E8 Joules.

 Using our 50,000 watt solar generator, that would only take 3.4 hours to generate the required energy(!) One question though, the energy needed in this case would be mechanical rather than thermal in mechanically raising the ice to the surface. What would the conversion efficiency be? Because of the quite high temperature of 3,000°C, by the Carnot Law the conversion efficiency could be quite high, certainly over 90%.

 Because the energy requirements for the mechanical lifting method are comparatively low we might even allow the fuel burn method of supplying the power rather than using solar thermal. Our needed total energy now is 6.4E8 joules. Using the calculated energy we used for a hydrolox engine of 11.5E6 J/kg of propellant, that would only require 6.4E8/11.5E6 = 57 kg.

 However, a problem with hydrolox with long space missions is boiloff. There is research in reducing it but whether it can be reduced enough for a misson of 3 to 4 year travel time through space is uncertain. So we'll estimate it using storable hypergolic propellants, same as used for the propulsion stages at Jupiter. In vacuum these can have 3,200 m/s exhaust velocity. This can give (1/2)*3,200^2 = 5.12E6 J/kg energy. Then it would take 125 kg of the storable propellant. This would still be doable for a 1,000 kg spacecraft payload. 

 The author of the "Calculating the Required Energy of Drilling into Europa" page does not prefer the mechanical lifting method, preferring to use the melting ice method eventhough it would take 2 orders of magnitude more power. This is because with a mechanical lift it may have a tendency of breakdwon operating in such low temperatures over long time.

 However, as the previous calculation using the solar thermal generator above showed it might be it would only take on the matter of hours. This would certainly reduce the likelihood of breakdown.

 Note also using the fuel-burn method of generating power, the moving exhaust itself could be used to raise the ice to the surface, thus elimating the issue of mechanical breakdown of the lifting method.

 There is another issue though for raising the ice to the surface without expending extra energy to melt it. Ice is brittle so likely would require low energy compared to the energy needed to raise to the surface to break it up. This is the case on Earth. However for the extreme level of ice compaction of Europa the ice would be denser so might be harder to break up. Experiments would need to be done to determine this.

  That discussion was for the 1st method of drilling down of mechanically raising the ice to the surface.. For the second method of only raising the ice to sublimatioin temperture of -75°C at first glance that might appear to be preferable. However, the energy of sublimation, the energy required to sublimate from ice to gas is so high, about 10 times higher than that just to melt it, it winds up taking more total energy than raising the temperature of the ice to the melting point of 0°C.

 So we'll consider the 3rd method of melting the ice and then using analogous methods as in the IceCube experiment. The calculation of the energy in this case is 1.2E13 but this was for a 1-meter wide drill hole and for a 25 km drill depth. So for our 6 cm wide drill hole down only 15 km the energy required would be: 1.2E13*(6/100)^2*(15/25) = 26E9. Using 50 kW solar thermal power, this would only take about 6 days. 

 Actually, in his calculation the author of the "Calculating the Required Energy of Drilling into Europa" page used a constant temperature of  -160°C for the ice that had to be raised to 0°C for melting. But since at the water level below the ice, the temperature will already be at about 0°C, perhaps a little less for salt freezing point depression, the temperature will gradually decrease linearly from 0°C to -160°C at the surface. So the calculation needed for the energy needed for the temperature change can be done by using the average of -80°C. This cuts the energy required for raising the ice to the melting point by about half. However, the energy for the phase change from ice to liquid will still be the same, resulting in the total energy being in the range of 75% of the estimated energy above. 

 Also, importantly, in comparison to the IceCube experiment drilling method, which took place in Antarctica at -50°C, an average temperate of -80°C on Europa is only moderately far from -50°C, compared to the -160°C temperature at the surface of Europa, which gives us confidence the energy requirements would be in line with those of the IceCube experiment.

 The author of that page prefers this melting method and we now have a good point of comparison to the IceCube experiment to have good confidence that it can actually work. As I mentioned before a great point in its favor is the quite short drilling time of only a fews days compared to the months to a year estimated for other proposals.

 Still, I am intrigued by the low energy requirements of  just mechanically raising of ice to the surface without melting, especially if using the exhaust from fuel-burn method of raising the ice to the surface, since this could shorten the drill time down even further to hours instead of days.

   Robert Clark 

 

  

Low cost Europa lander missions.

Copyright 2015 Robert Clark

  

 NASA has proposed funding for a future orbital mission to Europa. This is expected to have a billion dollar cost. A NASA-funded lander mission to Europa was expected to be too expensive. University of Arizona researcher Christopher Impey suggests doing privately funded missions to Europa:

SUNDAY, FEBRUARY 8, 2015
Let’s Send a Private Mission to Europa, Expert Says.
http://www.astrowatch.net/2015/02/lets-send-private-mission-to-europa.html

 Indeed, by following the commercial space approach an actual lander mission, not just orbital, can be mounted for costs in the range of one of NASA's lowest cost Discovery-class missions.

 Some observations by the Hubble telescope were that Europa may have plumes like Enceladus though those observations have not been confirmed. If it does, then it may be the subice ocean on Europa could be reached simply by traveling though the fissures, like on Enceladus, not requiring melting through the ice.

 For getting funding for a privately-financed mission, imagine how much interest there would be among the public if we could actually access this subsurface ocean. As a point of comparison the Mars Pathfinder missions web site caused such overloads, with 40+ million hits per day, that some mirror sites crashed or had to have access limited:

Traffic on Mars
by Chuck Toporek
Asst. Managing Editor
Web Review
However, the most interesting and little known fact about the amount of traffic to the mirror sites comes from France, where the government actually pleaded with computer users to stop accessing the two Mars Pathfinder mirrors. You see, the phone systems in France carry all of the Internet traffic in the country, so when people started visiting the mirror sites at VisuaNet and Le Centre National D'Etudes Spatiales (CNES), they tied up the phone lines and basically disabled the country.
http://mars.jpl.nasa.gov/MPF/press/webreview/index4.html

 Private companies that provided funding could be allowed to advertise on the mission web site.

Mission Delta-V requirements.

 The spacecraft first has to be sent on a trajectory towards Jupiter. This requires a delta-v of 6.3 km/s. Following a Hohmann trajectory it takes about 2.7 years to arrive at Jupiter. Aside from this Jupiter transfer delta-v, it will need to be placed into Jupiter/Europa orbit on arrival, and then sent towards a landing on Europa. According to this report this will require a delta-v in the range of 3.9 km/s:

European Cryo-Ocean Exploration Submersible (ECOES).

Preliminary Design Report. 

http://www.lpl.arizona.edu/~jmoores/ECOES.pdf

 We'll use a cryogenic, hydrogen-fueled stage for the injection into a trajectory towards Jupiter. And because of the long travel time, we'll use storable (hypergolic) propellants for the propulsive maneuvers at Jupiter.

Falcon 9 v.1.1 sized launcher.

 The expendable version of the Falcon 9 v1.1 has a payload to LEO of ca. 16.6 metric tons (mT). We'll use the Ariane H10-3 hydrogen-fueled upper stage for the Jupiter trajectory insertion. It has a 11.86 mT propellant mass, 1.24 mT dry mass, and 445 s Isp. Then it can carry 2.4 mT to the 6.3 km/s delta-v needed for the flight towards Jupiter:

445*9.81ln(1 + 11.86/(1.24 + 2.4)) = 6,324 m/s

 For the stage, at Jupiter we'll use the Integrated Apogee Boost Subsystem (IABS) stage.

 An artist's concept of a DSCS satellite being boosted by the IABS. Photo: U.S. Air Force

 

 This is a small kick-stage used to put geosynchronous satellites in their final orbits. It has a 1,578 kg gross mass and 275 kg dry mass, for a 1,303 kg propellant mass, and a 312 s Isp. Then this could provide a 220 kg spacecraft with the 3.92 km/s delta-v needed to land on Europa:

312*9.81ln(1 + 1303/(275 + 220)) = 3,947 m/s. 

 The Falcon 9 v.1.1 costs in the range of $56 million, the Ariane H10-3 cryogenic stage costs in the range of $12 million and the IABS stage costs in the range of $15 million, for a ca. $83 million launch cost.

 For a model of a low cost lander we might use the Mars Pathfinder mission. This weighed only 264 kg for the lander plus 10.5 kg for the rover. The development cost for the lander was less than $150 million. The development cost of  $150 million is quite low for a planetary mission. However,  privately financed it would be even less than that, perhaps as much as a factor of 10 cheaper.

  SpaceX was able to develop the Falcon 9 at a 90% (!) saving off  the development cost of a fully government-financed launcher of similar size. Planetary Resources Inc. plans to produce imaging satellites at a fraction of the usual cost.

Arkyd 100 space telescope.

 With mission costs this low we might want to produce a separate orbiter mission at Europa. As models for this we might use the small Mars orbiters Mars Odyssey and Mars Climate Orbiter.

Falcon Heavy sized launcher.



 The Falcon Heavy will allow a larger payload to be transported to the Europan surface. It is expected to be able to carry 53 metric tons to LEO. We'll use two Centaur stages together for the injection into a trajectory towards Jupiter. For the maneuvers at Jupiter, we'll use the storable propellant stage Delta K. This has a 6 mT propellant load, 0.95 mT dry mass, and 319 s Isp. Then it can provide a 1 mT spacecraft with the 3.9 km/s delta-v needed for the Europa landing:

319*9.81ln(1 + 6/(0.95 + 1)) = 4,397 m/s.

 The Centaur has several incarnations. It's propellant load is in the range of 20 mT, dry mass ca. 2 mT, and Isp ca. 451 s. Then two Centaurs together could provide the 6.3 km/s delta-v needed for the Jupiter flight carrying the 7.95 mT total mass of the Delta K stage + Europa lander:

451*9.81ln(1 + 40/(4 + 7.95)) = 6,500 m/s.

  The Falcon Heavy will cost in the range of $125 million. The Centaurs cost in the range of $30 million each and the Delta K stage costs ca. $4.35 million. Then the total launch cost will be in the range of $189.35 million.

 As a model of a 1 metric ton lander we might use the Mars Curiosity rover. This is a $1 billion mission however. The commercial space approach however should be able to produce a similar size spacecraft for a fraction of this cost.

 

   Bob Clark 

 

UPDATE, February, 20, 2015:

 The web traffic to the NASA web site for the Mars Exploration Rovers was even more extraordinary, measuring in the billions of hits:

NASA’s Web Site for 2005
By Digital Trends Staff — January 7, 2005
The U.S. National Aeronautics and Space Administration Web portal continues to drive high traffic numbers — more than 17 billion hits in 2004, report both NASA and Speedera Networks, a leading global provider of on-demand distributed application hosting and content delivery services. Speedera delivers content from the space agency’s portal to visitors seeking access to the site from around the world. Popular events on the NASA Web site, including the ongoing Mars Exploration Rover mission entering its remarkable second year, as well as upcoming major projects such as the launch and comet encounter of NASA’s Deep Impact satellite mission in 2005, are expected to drive continued high levels of traffic, according to NASA officials.
http://www.digitaltrends.com/computing/nasas-web-site-for-2005/

 It was estimated there were 142 million visits to the site during this period. So the question is how much advertising could be sold for a site this well visited?

Sample Return Missions from Enceladus, Europa, Titan, Ceres, page 1.

Copyright 2014 Robert Clark 

 Gravity measurements from Cassini have provided further evidence that Enceladus has a subice liquid ocean. It is being regarded now as a prime target in the search for extraterrestrial life. The question is how to reach that ocean through what may be 40 km of ice. There have been various proposals for drills. However, NASA has modeled the plumes seen to arise from the "tiger stripes" on Enceladus as coming from vents that attach to the ocean below. Then a simpler method may be to reach the ocean by traveling through these vents. 

This graphic shows how the ice particles and water vapor observed spewing from geysers on Saturn's moon Enceladus may be related to liquid water beneath the surface. The large number of ice particles and the rate at which they are produced require high temperatures, close to the melting point of water. These warm temperatures indicate that there may be an internal lake of liquid water at or near the moon's south pole, where the geysers are present.

http://www.nasa.gov/mission_pages/cassini/multimedia/cassini20080207.html

 In this model the temperatures don't have to be particularly high, just near the melting point.

 This method may work to reach subsurface liquid water for other outer solar system bodies expected to have them such as Europa, Titan and Ceres.

 As a feasibility test we might try it to explore subsurface though deep-sea hydrothermal vents here on Earth. 

Deep-sea vent biogeochemical cycle diagram.

 According to this model the temperatures might reach a maximum of 400 °C. If we can develop a robot to travel through these conditions quite likely it would also work in the conditions for the vent systems of these outer solar system moons.

In an upcoming blog post I'll discuss how the Falcon Heavy at a 53 metric ton(mT) payload capacity and the first version of the SLS at 70 mT could each be used to conduct sample return missions from these outer solar system moons.

     Bob Clark  


Update, April 27, 2014:

 At the Humans 2 Mars 2014 conference it was mentioned "white smokers" during an astrobiology session. These are lower temperature than the "black smokers" so might be easier to explore internally:

White smokers are seafloor hydrothermal vents that are cooler than black smokers. They deposit light-colored silica minerals as well as some sulfides.

https://web.archive.org/web/20130329102456/http://geology.about.com/od/geoprocesses/ig/hydrothermal-features/white-smoker.htm

Since they are smaller however we would need smaller robots to explore them.

UPDATE, February 9, 2015: 

 JPL is investigating robots that can explore fissures in volcanos. They are also considering how they could be used to travel to the subsurface through fissures on worlds such as Europa and Enceladus:

News | January 7, 2015
NASA Robot Plunges Into Volcano to Explore Fissure.

http://www.jpl.nasa.gov/news/news.php?feature=4431