Why is it so difficult to get to Pluto?
Pluto is the furthest celestial body a spacecraft has reached, this dwarf planet is more than
6 billion kilometers from Earth, and the only spacecraft that has managed to observe it directly
was New Horizons on July 14, 2015. However, this ship did not enter orbit around Pluto;
he observed it once and continued on his way to the far reaches of the solar system,
but why spend so many resources just for a straightforward approach to Pluto?
Let's find out! The furthest of all
For many years Pluto was considered the ninth planet in the solar system and the farthest of
all. Located at the far reaches of the realm of the Sun, it seemed that it would take centuries
for humanity to reach this small world. However, the first opportunity to visit Pluto came much
earlier than most scientists imagined. It was the year 1964 when the scientist
of the JPL laboratory of NASA called Gary Flandro realized that between 1976 and 1978, there would
be a gap of approach between the gaseous planets, so if a space exploration probe was launched
on those dates, it could visit most of the outer planets using a series of successive gravitational
assists taking advantage of the unusual planetary alignment that occurs almost every two centuries.
Shortly after, NASA launched an ambitious project called Grand Tour,
which would be starring two twin TOPS probes (although, in principle, they should be four).
One of the probes would be launched in 1976 or 1977 to explore Jupiter, Saturn, and Pluto,
while the second would visit Jupiter, Uranus, and Neptune. According to NASA's plans, the
encounter with Pluto would occur in 1985 or 1986. After analyzing the ambitious Grand Tour project,
NASA concluded that its cost would be too high, so the Grand Tour project
and the TOPS probes were canceled. Shortly after, NASA would launch a new, more modest,
and less expensive project, and from there would arise the famous Voyager exploration probes.
Voyagers were initially scheduled to follow the same trajectories as the Grand Tour project,
and NASA retained the option of sending Voyager 1 to Pluto after it visited Saturn. If the mission
had been approved, Voyager 1 would have flown by the Pluto system in the spring of 1986. Instead,
NASA preferred to send the probe close to Titan, Saturn's largest moon, rather than Pluto. So once
again, any visit to Pluto was canceled. Why were missions to Pluto canceled
again and again? The reason is simple; Pluto is too far away.
A challenge for the technology of the time The Voyager probes did not have solar panels since
they were intended to explore distant planets; in those regions, the solar radiation was very low,
and a solar panel could not supply enough energy. Instead, the probes had nuclear batteries that
produced electrical energy from the thermal radiation emitted by a radioactive compound.
NASA concluded that due to natural wear and tear, this source of radioactive energy could
eventually be exhausted long before reaching Pluto, so instead of losing the spacecraft,
it was decided to take the opportunity to visit Titan. No one expected that after visiting Titan,
Voyager's power source would still work; it was simply a stroke of luck.
After these missions, NASA declared that Pluto is a lonely, small and distant world,
so the ships that visit it in the future necessarily had to be complex and very expensive.
Many scientists thought it was better to spend that money on studying the giant
planets and their dozens of satellites, so the ninth planet would have to wait.
During the 80s, no serious proposal to explore Pluto emerged, although there were undoubtedly
exciting projects. The most curious of these was the Interstellar Precursor Mission (IPM)
study of the Jet Propulsion Laboratory (JPL). The IPM mission aimed to send a massive probe to
the heliopause, the solar system's edge where the solar wind gives way to the interstellar medium,
in a relatively short time. The probe would have a mass of about 90 tons; yes,
you heard correctly, 90 tons! That is, the heaviest exploration probe in history and,
therefore, should be assembled into Earth orbit by more than five Space Shuttle missions.
This spacecraft would be equipped with a nuclear reactor and use an electric propulsion system
(NEP) with ion engines. And what relationship did IPM have with Pluto? well, this had to carry
a probe to study the ninth planet that would separate when passing through its vicinity.
This orbiter would be similar to the Galileo probe for studying Jupiter. It would use a propulsive
stage, that is, a rocket, to reduce its high speed and place itself in orbit around Pluto,
which would hopefully take place during the first decade of the twenty-first century.
As you may be imagining, this never saw the light since, once again, the cost of such a
project would be exorbitantly high. Sparked the spark of curiosity
In 1989 Voyager 2 had its encounter with Neptune; this event revived interest in a mission to Pluto
since this was the only planet left to explore. In addition, Triton, Neptune's largest moon,
had turned out to be a complex world with an atmosphere, polar ice caps, and nitrogen geysers.
Observations from Earth indicated that Triton and Pluto shared a common origin in the Kuiper belt
and, therefore, must be very similar, especially since it was discovered in 1988 that Pluto was
also shrouded in a tenuous atmosphere. In addition, in 1978, Pluto's first moon,
Charon, was discovered, so a probe could now explore two worlds for the price of
one. A mission to Pluto once again climbed the scientific community's priorities.
One of the first proposals was the Pluto 350 mission. The name referred to the weight of the
spacecraft, which should not exceed 350 kg, including the radioisotope generator (RTG),
to produce electricity. Pluto 350 was born two months after Voyager 2's encounter with
Neptune. It was to include only four instruments: a camera, an ultraviolet
spectrometer for the study of the atmosphere, a radio experiment to observe the atmosphere mainly,
and an instrument for plasma analysis. Among the architects of the mission was a
planetary scientist named Alan Stern, who would be a key piece in the history of Pluto's exploration.
Scientists feared that the dwarf planet's atmosphere would freeze as the planet moved away
from the equinox that had occurred in 1987, so the launch should take place as soon as possible.
Like the rest of the spacecraft proposals to Pluto, the Pluto 350 mission was to fly by
Jupiter to perform a gravitational assistance maneuver and thus reduce the flight time by two
or three years, depending on the launch window. To place the ship on a direct trajectory to the
gas giant, the mission had to be launched by a large rocket, a Titan III or a Titan IV,
which was the most potent American launcher at the time. However, this
requirement increased the cost of the mission. Paradoxically, the Pluto 350 mission suffered
rejection from NASA for being too simple. This is because many scientists and engineers claimed
that launching a 350 kg probe into the outer solar system was a recklessness that had no
chance of success, considering that previously the Voyagers had had a mass at launch of about 800 kg.
In other words, NASA preferred a more complex and expensive mission,
but with a guarantee of success, than a simple mission, but with the possibility of failure.
Missions that never saw the light of day In an era of meager budgets, NASA focused
on simple flyby missions. In 1992, JPL's Robert Staehle went further and announced the Pluto Fast
Flyby (PFF) mission. A tiny mission compared to anything that had been done until then.
If Pluto 350 were once a small probe, PFF would be tiny since its mass would be less than 150
kg. A few years before, few believed such a probe could be built, but with the constant
cuts to NASA's budget, these new low-cost missions became almost the only option.
Years later, NASA rejected the Pluto Fast Flyby mission proposal and replaced it
with a new mission called Pluto Express. Since David Jewitt and Jane Luu discovered
the first body in the Kuiper belt in 1992, it was becoming increasingly apparent that Pluto
was not a planet like the rest but a member of this new family of trans-Neptunian objects.
For this reason, the mission would be baptized as Pluto Kuiper Express (PKE). At 175 kg,
PKE would be slightly larger than Pluto Fast Flyby (140 kg) and carry 9 kg of scientific instruments,
although its design was similar. Ultimately, both Pluto Fast Flyby
and Pluto Kuiper Express were canceled due to budget cuts. But a mission to Pluto remained
a scientific priority as the launch window from 2001 to 2006 was inexorably approaching,
and then there would be no other chance. So in desperation, in 2000, NASA created
a public contest to choose a mission to Pluto. This strategy had worked very well on low-cost
missions called Discovery, but never before had such an expensive probe been attempted. Since the
mission to Pluto required a more expensive mission than a Discovery-type mission but cheaper than a
Flagship mission, NASA decided in 2002 to create the New Frontiers category for this type of probe.
This is how on February 5, 2001, the winning proposal was the New Horizons. At first, it would
carry four scientific instruments, these would be: - PERSI (which included the Alice
ultraviolet spectrometer - The MVIC color camera
- The LEISA infrared spectrometer - REX (a radio experiment)
- LORRI (a black and white telescopic camera) - PAM (for the study of particles)
To reduce the mass and cost of the probe, the corners of the triangular structure were
'trimmed,' and the diameter of the antenna had to be reduced from 3 to 2.1 meters. The final mass
of the vehicle reached 478 kg. The total cost of the mission would be $646 million in 2014.
The probe was launched from Cape Canaveral on January 19, 2006. New Horizons approached
Jupiter between February and March 2007 to take advantage of the planet's gravitational assistance
and thus acquire a speed difference of about 4,023 m/s (14,482 km/h).
In July 2013, the probe sent back the first images in which Pluto and its largest satellite,
Charon, can be distinguished as separate bodies. As New Horizons approached Pluto,
the images sent back gained resolution. Until the day everyone expected on July 14,
2015, the New Horizons probe passed 12,500 km from Pluto's surface at a
relative speed of 49,600 km/h, taking the sharpest images it had ever seen of what
was once the ninth planet in the solar system. In addition to photographing Pluto, The probe
also sent tons of information that has served to discover all the mysteries of this celestial body;
thanks to this, today we know that Pluto is a vast ball covered with ice with recent geological
activity and that it could contain water. After the Pluto flyby, the New Horizons
probe continued its journey to the solar system's far reaches; to date, no other
mission has managed to reach this distant world. Do you think we will ever revisit Pluto? Let us
know your opinion in the comments.