American Scientist

October 4, 2017, marks the 60th anniversary of the launch of Sputnik, the first artificial satellite. It operated for only 92 days and did not carry any specific scientific equipment, but its transmitters generated radio signals heard around the world as the "beep…beep…beep" that marked the beginning of the Space Age. Over the years, the impact of Sputnik continued in the literal "sputniks" (which is Russian for satellite) that followed, in the broader development of the Soviet and Russian space programs, and ultimately in the entire program of cosmic exploration that the tiny orbiting ball initiated.

The sheer magnitude of the Sputnik effect makes it difficult to analyze in a coherent way. As scientists whose lives are connected with space research and exploration, we are inclined to consider the event primarily as a scientific achievement. It is true that Sputnik itself was not much of a scientific spacecraft, but its launch was announced as a contribution to the International Geophysical Year (IGY), an international program from July 1957 to December 1958 with science exchange and activities to better understand the planet Earth. Two satellite projects in the United States were likewise developed in the context of the IGY. The resulting Vanguard and Orbiter (later Explorer) projects emerged as rivals, not just to the Sputnik program but also occasionally to each other. Modern space exploration emerged from this multifaceted rivalry.

In the USSR, the project to build a satellite officially started in the beginning of 1956. Work on “Object D” (the classified designation of the future Sputnik 3) was assigned to engineer Sergei Pavlovich Korolev’s Special Design Bureau No. 1 (OKB-1), then the leading Soviet organization for the development of rockets. The scientific payload was designed and developed by several scientific institutions under the umbrella of the USSR Academy of Sciences. At the same time, a special commission for Object D was established under Mstislav Vsevolodovich Keldysh, vice president of the academy, an outstanding scientific leader, and a close friend of Korolev. Keldysh became the leader of the scientific side of the Soviet space exploration program.

Object D was intended to carry scientific experiments with dedicated instruments. In late 1956, however, it became clear the project would not meet the target launch date in the fall of 1957. Instead of postponing the launch, Korolev decided to replace Object D with another, much simpler spacecraft, designated PS-1 (prosteishyi sputnik 1, essentially “the simplest satellite”). The decision was motivated by the fear that American rocket engineers would be the first to launch a satellite: The Vanguard project was under way, and even though it was not ready for launch, the sense of rivalry was intense. So Sputnik 1—a modest ball with antennae, batteries, a radio transmitter, and little else—was created to be the first satellite to orbit Earth. To some extent, it was an ideal symbol for the first humanmade body in space.

Despite its simplicity, Sputnik 1 also served science. The USSR built a network of observational stations throughout the country to track its path. Based on those observations, researchers obtained new information on the atmospheric density at Sputnik’s altitudes, and a new branch of science was conceived—space geodesy. Without any specific scientific equipment, however, Sputnik 1 was considered by many to be a mere toy sent for the sake of the space race. Its successors, Sputnik 2 and Sputnik 3, were much more scientific in their missions. On November 3, 1957, Sputnik 2 carried the dog Laika, the first living being in space. Sputnik 3 was the actual Object D, which finally launched on May 15, 1958.

Sputnik 3 carried 12 instruments (weighing 968 kilograms out of a total of 1,327 kilograms for the entire satellite) to study solar-charged particles, electrical and magnetic fields in space, ion content and density of the upper atmosphere, and the population of micrometeoroids. Sputnik 3 data showed that there are two radiation belts around the Earth: The inner belt consists primarily of protons, whereas the outer one has a mostly electron population. Data from Sputnik 3 supported the idea that particles precipitating from the belts were the cause of auroras and ground-level electrical discharges. From there, the picture of Earth’s space environment started to assemble. The last of the formally designated Sputnik missions—Korabl-Sputnik 5—in 1961 carried a dog, Zvezdochka, along with a realistic mannequin named Ivan Ivanovich.

Sputnik 2 and Sputnik 3 marked two sharply divergent styles of space exploration: crewed (if only with dogs) versus automatic. The first approach was more appealing to the general audience, which got them used to the idea of future colonization of space. The second strategy implied that remote-sensing techniques and special robots could fully replace human beings in space. Later, when the real hostility of the space environment was assessed, the idea of extended human space travel seemed less viable than even at the time of Yuri Gagarin—the first human in space—and the Apollo program. It is now known that humans can live and work in near-Earth space; it is less clear what tasks can be done only in space and only with human hands.

The greatest opportunity Sputnik 1 and its many descendants gave to science is the opportunity not to merely observe, but to run active experiments in interplanetary (even interstellar) space or on the surface of other planets and bodies. We are nowhere near the limit of this opportunity, and this is what gives space science its constant boost.

Planetary Space Race

Just four years after Sputnik 1, the first spacecraft were launched to fulfill the most urgent desire of space visionaries: to explore other worlds, starting with the Moon, Mars, and Venus. It was only natural for the first space explorers to study the outer worlds with the aim to use them for the sake of humanity. The environment on the surfaces of our neighboring worlds turned out to be far from hospitable, though. That might be why the original impetus for space exploration as a human adventure subsided rather quickly. On the other hand, scientific interest has not subsided at all.

In parallel with the human space race to the Moon, a more Sputnik-like planetary space race developed starting in the 1960s. In this competition, the USSR focused its efforts on Venus. The Soviet Venera 7 lander was the first to reach the surface of the planet in 1970 and study its hostile environment. Later, in 1975, Venera 9 transmitted the first panorama of the Venusian surface. These images, together with those obtained by Venera 13 and Venera 14 in 1982, remain the only direct views of Venus. Besides this accomplishment, the Venera probes conducted a great number of experiments to study the composition of the planet’s surface and atmosphere, its weather patterns, and its electromagnetic environment. The first hints of lightning on Venus were detected, a discovery later confirmed by the Venus Express orbiter from the European Space Agency (ESA).

The United States, on the other hand, had its greatest early achievements in the studies of the Red Planet, Mars. Those initial successes led to a long chain of missions, running from Mariner 4 in 1964–65 to the twin Viking landers of the 1970s to the Opportunity and Curiosity rovers now in operation, along with the upcoming InSight lander and still-nameless Mars 2020 rover. Overall, Soviet Martian missions were far less successful. The Soviet Mars 3 lander made the first landing on Mars in 1971, but it worked for only 20 seconds before going silent. The affiliated Mars 3 orbiter successfully mapped the plasma environment around Mars, showing it resembles that of Earth. The subsequent Mars 4, 5, 6, and 7 missions, however, mostly or completely failed.

A major early discovery from the planetary space race was that neither Mars nor Venus showed any evident signs of life; instead, they presented surprisingly hostile environments. A notable related finding was that Earth’s closest planetary neighbors show extreme variants of greenhouse-effect evolution. On Venus, a thick carbon-dioxide atmosphere, along with slow rotation and proximity to the Sun, have led to enormous heating. The temperature of the surface is around 400 degrees Celsius, the pressure is 93 times higher than on the Earth, and the sky is cloaked with clouds consisting primarily of sulfuric acid.

On Mars, with an exceedingly thin atmosphere, we observe an opposite outcome: The atmosphere is very thin and cannot accumulate solar heat, so the average temperature is low, around –40 degrees Celsius on average. Data from the U.S. missions have supported the idea that Mars initially had large reservoirs of water that then escaped into space, leaving the planet bare and dry on the surface (except for its polar regions), though with significant subterranean deposits of water ice and carbon-dioxide ice.

The Mariner and Venera probes revealed a likely explanation for these environmental extremes: Neither Mars nor Venus has an appreciable magnetic field. It is assumed that both planets lost their water due to photochemical processes and interaction with the solar wind. Ultraviolet rays split apart water molecules and, in the absence of the kind of powerful field that protected Earth, charged particles from the Sun then carried away the hydrogen. A similar process may limit the habitability of planets orbiting other stars as well.

The original impetus for space exploration as a human adventure subsided rather quickly. On the other hand, scientific interest has not subsided at all.

• Facebook
• Twitter

What makes Mars different from other planets is that, despite its obvious hostility, it is the only planet where human beings could plausibly survive without extreme protective hardware. That trait is a major reason why Mars is the most frequently visited planet. Besides those launched by the United States and Russia, additional Mars missions have come from Europe, Japan, China, and India, and many more are to come in the near future.

Another focal point of post-Sputnik robotic exploration was the Moon. Despite a half-century of ongoing studies, key questions remain unresolved. Most notably, there is the problem of the Moon’s origin. The leading theory says that the Moon emerged after a great impact between the proto-Earth and a Mars-size planetary body. Yet some details about the Moon’s composition and angular momentum do not fit; some evidence still favors the opposing theory, that the Moon and the Earth formed simultaneously but separately.

During the 1960s and 1970s, both USSR automatic interplanetary stations (Luna 16, 20, and 24) and U.S. Apollo astronauts targeted the Moon’s equatorial regions. That approach, although pragmatic, missed some intriguing aspects of lunar geology. Later remote-sensing data from the U.S. Clementine and Lunar Prospector missions in the 1990s determined that the Moon’s polar regions may differ significantly from its equatorial zones. Polar areas seem to contain a notable amount of volatiles (easily vaporized substances), especially in permanently shadowed craters. There are apparent deposits of water ice in the shallow subsurface of these regions, which makes them appealing locations for establishing a possible lunar base, either manned or robotic.

Into the Deep

By the 1990s, the nearest neighborhood of the Solar System was inspected more or less thoroughly, even though there was still a lot to learn. The regions outside the Martian orbit and closer to the Sun than Venus are less explored. There have been only two full-fledged missions to Jupiter (Galileo and Juno, both by NASA) and only one dedicated to the study of Saturn (Cassini-Huygens, a NASA/ESA endeavor). The two Voyager missions gave a “portrait gallery” of the outer planets and their satellites; New Horizons flew past Pluto in 2015 and now is headed to a distant Kuiper Belt object, 2014 MU69.

Successors of the early Sputniks have visited almost every major destination that can be reached within a human  lifespan using current technology.

• Facebook
• Twitter

Human exploration of the deep solar system is out of the question for now, so the automated model of Sputnik 3 prevails. Two spacecraft have visited Mercury: Mariner 10 (1974–75) and MESSENGER (2005–2015), both by NASA. The innermost planet is interesting for its high density and strong magnetic field. Despite Mercury’s proximity to the Sun, like the Moon it has volatiles, and most probably water ice, in its shallow subsurface.

One of the largest international explorations of the first decades of the Space Age was aimed not at a planet but at a much smaller object: the famous Comet Halley, which is just 15 kilometers wide. The comet’s last close approach to the Sun occurred in 1986. As that date approached, the USSR, the ESA, and the Japan Aerospace Exploration Agency (JAXA) decided to send a spacecraft. The “Halley Armada” included two Soviet probes (Vega 1 and Vega 2), two Japanese contributions (Sakigake and Suisei), and the ESA’s Giotto spacecraft.

In March 1986 five spacecraft passed through Comet Halley’s coma, the cloud of gas and dust surrounding its solid nucleus. The level of coordination among agencies was so great that data on the position of the comet from the Soviet Vega 1 and Vega 2 were transmitted in real time to Giotto’s operators, who used them to more precisely target the probe. As a result, Giotto was able to fly just 596 kilometers from the comet’s nucleus. Meanwhile, the Vegas’s instruments gave experimental evidence of the complex interaction between the solar wind and the comet. Plasma structures around Comet Halley were oddly reminiscent of those around Mars and Venus, because the comet has no intrinsic magnetic field.

The Halley Armada marked the beginning of more intensive exploration of smaller Solar System bodies, which now are known to be far more diverse than had been assumed on the basis of prior Earth-based observations. The armada also established a collaborative, international approach that moved past the geopolitical rivalry that had inspired the first Sputniks. To our mind, the apex of the small-body missions (for now) was the Rosetta project, which orbited comet 67P/Churyumov-Gerasimenko for almost two years and landed the Philae probe on its surface.

At the other extreme is the largest object in the Solar System: the Sun. Sputnik 3 pioneered the study of space plasmas, and solar science has advanced greatly since then. A subsequent series of small Soviet spacecraft called Kosmos helped piece together a comprehensive picture of Earth’s magnetosphere, its interactions with the upper atmosphere, and the physics of radiation belts and aurora regions. Gradually, we came to think of Earth as a planet within a plasma bubble created by the terrestrial magnetic field.

The geomagnetic field protects everything on Earth’s surface, including us, from solar and galactic cosmic rays—fluxes of energetic charged particles. This natural shield probably played a major role in the emergence and evolution of life. Nevertheless, large bursts from the Sun, called solar mass ejections, can cause the magnetosphere to respond, allowing charged particles to penetrate deeper into it; such “guests” are potentially hazardous for near-Earth satellites. Another menace is the trapped radiation in the Earth’s radiation belts, which precipitates at high latitudes and can pose a danger for the pilots and passengers of high-altitude planes.

The Sun’s influence continues far beyond the orbit of Pluto, where solar wind meets with interstellar medium, creating two borders: the termination shock (where solar wind velocity decreases to subsonic) and the heliopause, or the border between the regions with dominating solar wind particles and alternatively that of the interstellar medium. This region was explored by the Voyager 1 and Voyager 2 probes, launched in 1977 but still active. After Sputnik 1, the flight of Gagarin, and Apollo, one must put the Voyager mission as the major milestone of space exploration successes.

Astrophysicists expected to find the Sun’s termination shock approximately 90 astronomical units (AU) distant from it, and the heliopause at 150 AU (where an AU is defined as the average distance from the Earth to the Sun). In the 2000s, the two Voyagers crossed the actual termination shock at 94 AU and 84.7 AU, respectively; then in 2012, Voyager 1 reached the heliopause at 121 AU. The discrepancies between models and measurements might be because of interactions between magnetic field lines, which tend to shrink and deform the volume containing the solar plasma.

If we think about space exploration as being about crossing the borders and pushing frontiers, then Voyager is perhaps the last, greatest achievement of the expansive phase that began with Sputnik 1 six decades earlier. For the first time, humanmade objects pushed through the Solar System and sensed interstellar space. It seems that the successors of Sputnik have visited almost every destination that can be reached within a human lifespan using current technology.

Russian Perseverance

There is an old proverb: “If you want to make God laugh, tell him about your plans.” Plans in Soviet and Russian space science have changed repeatedly in response to new discoveries, fashion, and, last but by no means least, financial realities. The heated political climate that spurred the early Sputniks had greatly cooled by the 1980s. Social and economic crises of the 1990s led to a decade-and-a-half hiatus in Russian planetary exploration. Only a few missions were launched after 1990, and we also suffered two tragedies of interplanetary missions: Mars 96 in 1996 (an orbiter mission) and Phobos Sample Return in 2011 (an attempt to collect samples from Phobos, Mars’s closer moon).

On the other hand, Russian scientists succeeded with the Interball multiprobe mission during the tough years from 1995 to 2001. Four spacecraft were sent into two types of orbits. One pair studied aurora regions around Earth; the other went far into the tail of the magnetosphere, where the solar wind blows Earth’s magnetic field into a long cone. Interball was among the first projects to make simultaneous measurements in different regions of near-Earth space. A similar approach was later adopted by ESA’s Cluster and NASA’s Magnetospheric Multiscale (MMS) missions. There were a few other, more recent Russian-led projects, including the innovative Spektr-R, a space-based 10-meter radio dish that can link with its counterparts on the ground to create the equivalent of a 350,000-kilometer telescope.

More often, Russia has built on the post-Sputnik international spirit of the Halley Armada. Russian scientists in the 2000s participated in ESA’s Mars Express and Venus Express, as well as NASA’s Mars Odyssey, Lunar Reconnaissance Orbiter, and Curiosity. Russian-built neutron detectors discovered huge deposits of water ice below the Martian surface and proved that some regions of the Moon are up to 4 percent water by weight, a surprising and exciting discovery. Russia also participates in the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), an international x-ray observatory under ESA’s leadership. Russian-directed research with INTEGRAL led to the discovery of vast clouds of electrons and positrons (their antimatter equivalent) annihilating each other at the center of the Milky Way.

One of the most ambitious current collaborations is ExoMars, a two-part effort between ESA and the Russian Roscosmos State Corporation for Space Activities since 2013 to search for signs of past and present life on Mars. The first ExoMars mission, launched in 2016, consisted of the Trace Gas Orbiter (TGO) and Schiaparelli lander. TGO will perform a thorough study of Martian atmospheric trace gases, which may inform us about possible ongoing biological activity. TGO is currently circling Mars and will start its scientific mission once it reaches its final orbit in April 2018. The second ExoMars mission, to be launched in 2020, comprises a European rover and a Russian stationary surface platform that will extend the studies of geochemistry and possible biochemistry to the surface. The rover bears two instruments built in Russia; the descent module to land on Mars is provided by Roscosmos, as is the Proton launcher for this mission.

Russia is also contributing several instruments to the upcoming European-Japanese BepiColombo mission to Mercury. This dual-probe spacecraft aims to analyze the interior of the smallest planet, its interaction with solar wind, and the composition of its upper surface.

Object D ushered in a new age of cosmic studies, as astronomers finally could observe the sky in the whole range of photon energies, from radio to gamma rays. Russia’s space program is pressing ahead there as well. Most of the electromagnetic spectrum is invisible to observers on Earth, because our planet’s atmosphere effectively absorbs these photons. Spektr-RG, an x-ray observatory being developed jointly by Russia and Germany, bears two x-ray telescopes: eRosita (Germany) and ART-XC (Russia). Over its planned seven-year mission, it will provide the most complete census of massive galaxy clusters and supermassive black holes in the observable universe. Like BepiColombo, Spektr-RG is set for a 2018 launch.

In the 2020s, Roscosmos plans to participate in two major new space-plasma and solar missions. One, called Resonance, consists of several identical spacecraft that will orbit within a single “tube” of flux in Earth’s inner magnetosphere, closely monitoring interactions between particles and waves in this region. Such observations will enable new insights into space weather, which can disrupt communications and overload power lines on Earth. Interhelioprobe is a mission to send two identical spacecraft to within 45 million kilometers of the Sun, high out of the plane of the Solar System. No spacecraft has yet operated in these regions. Interhelioprobe is not expected to launch until after the end of the current Federal Space Program of the Russian Federation in 2025, however, so its future is especially sensitive to the divine laughter that often greets ambitious plans.

Back to the Moon

The Venera and Luna programs begun in the 1960s greatly expanded human understanding of the worlds closest to Earth, and yet many mysteries remain. It is only fitting then that Roscosmos’s future plans include a return to the Moon and Venus, this time starting with a much more sophisticated baseline of knowledge.

Key questions regarding Venus include why the greenhouse effect became so fierce there; what causes the upper layers of the atmosphere to move much faster than the planet’s rotation; and when geologic activity reshaped the surface with volcanic rock. For about a decade Russian scientists have developed blueprints for a lander, named Venera-D, that could survive on the surface for a much longer time that its predecessors—up to several days in the crushing heat. This project would include an orbiter and perhaps balloons as well. Venera-D has experienced many difficulties though and remains in the state of preliminary design. A joint Venus-mission science definition team with Russian and American participants is seeking a way to bring this project to life.

The more immediate Russian goal is a revived lunar program, harkening back to the earliest days of the Sputnik era. For planetary scientists, the Moon is a place to study the history of Earth’s formation and the early evolution of Solar System. The Moon is also a promising place to build a crewed scientific station beyond low-Earth orbit. It is close enough to be relatively safe, yet it is outside the Earth’s magnetosphere and the atmosphere and radio signals that interfere with many astronomical observations. An observatory on the Moon is a technologically viable project that could be implemented in the close future. Such a research station would almost surely be international because of its cost and broad appeal. The International Space Station offers a template for how a lunar base could be built.

Russia’s current plans—that word again—begin with two lunar landers, one orbiter, and one sample return mission before 2025, along with one rover after that. These will pave the way for crewed expeditions and eventually a full-fledged base, anticipated to have shift workers and extensive scientific facilities. The name of the new missions will bear the legacy of Soviet Lunas, which ended in 1976 with the Luna 24 sample return mission. The first in the new series, Luna 25, will be a lander to explore the southern polar regions of the Moon, an appealing location for a base because of its relatively high water content and favorable conditions for radio communication. Then comes a Luna 26 orbiter, which will test pole-to-orbit radio links and orbital operations. It will also scout sites for the next Luna 27 landing mission.

We envision Luna 27 as a truly international mission that will test systems for high-precision landing, hazard avoidance, and cryogenic drilling. This last task is crucial for understanding the composition of the lunar surface and its suitability as a resource for future astronauts. All of these elements are now under discussion with our European colleagues. Pushing the technology a step further, Luna 28 will deliver samples of lunar material with untouched volatiles back to the Earth where they can be studied more thoroughly. Luna 29, which will be probably launched after 2025, will deliver a Lunokhod (“Moon walker”) rover that can travel extended distances to collect interesting samples.

The incremental, housekeeping approach of the new Luna program is intended to fill the gap between crewed and automatic space exploration. In Russia as in the United States, human exploration has historically developed more intensely than fundamental science. That imbalance has been present since the very beginning of the Space Age. It spurred the triumphs of Apollo but also the long period of stagnation that followed. One of the greatest lingering challenges from the early Sputnik program is finding the right harmony between humans and machines.

Humans today are finally well equipped for working in space. The question is what can be done there, and a crucial part of the answer will come from science. Space is a unique laboratory with numerous opportunities as yet untapped. The genealogical tree of Sputnik shall continue further, and the next revision will be even more overwhelming to summarize than the one given here. That prediction is perhaps the only thing about space science we can be sure of.