What is the Space Mission Planning Advisory Group, and Why is It Important?

Humanity’s Global Shield

The solar system is a busy, dynamic place. Earth travels through a cosmic neighborhood filled with millions of rocky and icy bodies, remnants from the dawn of planet formation. Most of these objects, known as asteroids and comets, orbit the Sun peacefully. A small fraction are on paths that bring them uncomfortably close to our planet. These are the Near-Earth Objects (NEOs).

For most of human history, these objects were viewed as either celestial omens or, more recently, as a purely theoretical, science-fiction-style threat. This perception changed permanently on February 15, 2013. On that morning, a small, undetected asteroid roughly 20 meters across entered the atmosphere over Chelyabinsk, Russia. It exploded in the air with the force of nearly 30 Hiroshima bombs. The resulting shockwave blew out windows across six cities, injuring over 1,500 people.

The Chelyabinsk meteor was a global wake-up call. It demonstrated in vivid, undeniable terms that the asteroid threat is not hypothetical. Even a small object, too small to be detected by contemporary sky surveys, could cause significant regional damage and personal injury. What if it had been larger? What if it had exploded over a more densely populated city?

It became clear that planetary defense was a serious, practical issue for the 21st century. It was also clear that no single nation could or should bear the burden alone. Defending the planet requires a global effort, combining the detection assets, technical expertise, and launch capabilities of all space-faring nations.

In response to this recognized need, the international community, working through the United Nations, established two key bodies to coordinate Earth’s defense. One, the International Asteroid Warning Network (IADWN), was tasked with finding, tracking, and characterizing NEOs. The other, the Space Mission Planning Advisory Group (SMPAG), was created to answer the most difficult question of all: if we find one coming our way, what exactly do we do about it?

SMPAG (pronounced “sam-page”) is the international forum of space agencies that provides the technical “playbook” for deflecting a hazardous NEO. It is the nuts-and-bolts planning group, the engineering committee, and the strategic advisory board all in one, designed to turn a theoretical mitigation mission into an actionable, cooperative international plan.

The Asteroid Threat: A Clear and Present Danger

To understand SMPAG’s purpose, one must first understand the threat it was built to address. The danger from NEOs is a matter of statistics, physics, and time.

Defining the Menace

A Near-Earth Object is an asteroid or comet whose orbit brings it within 1.3 astronomical units (AU) of the Sun. One AU is the distance from the Earth to the Sun, about 150 million kilometers. This definition means their orbits can cross Earth’s path.

Within this group is a more specific classification: Potentially Hazardous Asteroids (PHAs). A PHA meets two criteria:

1. Size: It is larger than approximately 140 meters (460 feet) in diameter. An object of this size would cause catastrophic regional devastation, far beyond what was seen at Chelyabinsk.
2. Proximity: Its orbit brings it within 0.05 AU (about 7.5 million kilometers) of Earth’s orbit.

This 140-meter threshold was chosen because an impactor of this size or larger would have effects that are not just local but regional or even global. While scientists have found over 90% of the “planet-killer” asteroids (those 1 kilometer or larger, like the one believed to have caused the Cretaceous–Paleogene extinction event), it’s estimated that we have only found about 40% of the PHAs in the 140-meter class. Tens of thousands are likely still out there, their orbits unknown.

Modern Wake-Up Calls

The Tunguska event of 1908 is another powerful reminder. An object estimated at 50-100 meters wide exploded over a remote region of Siberia, flattening over 2,000 square kilometers of forest. Had this event occurred over London or Tokyo, it would have been one of the worst natural disasters in human history.

Chelyabinsk in 2013 was smaller but, in many ways, more alarming. It came from the direction of the Sun, making it invisible to ground-based telescopes, which scan the night sky. It highlighted a significant blind spot in our detection capabilities.

These events provide a clear, data-driven case for action. The threat is not one of if a major impact will happen, but when. Unlike any other natural disaster an asteroid impact is predictable given enough warning. And more importantly, it is preventable with modern technology.

Forging a Response: The Birth of SMPAG

The 2013 Chelyabinsk event occurred just as the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) was finalizing a set of recommendations on the NEO threat. The committee’s Action Team 14 (AT-14), which had been studying the issue for years, proposed a formal international framework.

The realization was that the problem had two distinct parts: finding the threat and neutralizing the threat. These two tasks require different tools, different experts, and different forms of cooperation.

Two Halves of a Global Shield

The UN-endorsed solution was to create two independent but interconnected groups:

1. The International Asteroid Warning Network (IADWN): IADWN’s job is to be the world’s “neighborhood watch.” It’s a virtual network that links the telescopes, observatories, and survey programs of different nations. Its members (like NASA‘s Catalina Sky Survey or the Pan-STARRS system) scan the skies, report their observations to the Minor Planet Center (MPC) for orbit calculation, and share data. IADWN is responsible for being the single, authoritative voice to confirm a credible impact threat and issue warnings to the UN and member states. It answers the questions: “What is it? Where is it? When will it hit?”
2. The Space Mission Planning Advisory Group (SMPAG): SMPAG’s job is to answer the question, “What do we do about it?” It was established in 2013 by the members of COPUOS’s Action Team 14 as a technical forum of national space agencies. Its mandate is to prepare for an international response to an NEO threat by laying out the technical options, coordinating mission concepts, and understanding the technologies required.

SMPAG is not a command-and-control center. It cannot order NASA or the European Space Agency (ESA) to build a spacecraft. Instead, it’s a planning body. It’s where the world’s leading space agencies meet before a crisis to agree on a playbook. By doing the preparatory work in advance, SMPAG ensures that if IADWN ever raises the alarm, the world doesn’t waste precious years debating how to respond.

Inside SMPAG: Structure and Membership

SMPAG is an association of space agencies and relevant government offices. It’s not a treaty organization but a forum for cooperation, operating by consensus.

Who Gets a Seat at the Table

Membership is open to any national space agency or governmental body with an active interest and capability in space missions. The group meets twice a year, with a rotating Chair.

As of the 2020s, the primary members of SMPAG include:

• Agenzia Spaziale Italiana (ASI) (Italy)
• Canadian Space Agency (CSA) (Canada)
• China National Space Administration (CNSA) (China)
• Centre national d’études spatiales (CNES) (France)
• Deutsches Zentrum für Luft- und Raumfahrt (DLR) (Germany)
• European Space Agency (ESA) (representing its member states)
• Indian Space Research Organisation (ISRO) (India)
• Japan Aerospace Exploration Agency (JAXA) (Japan)
• Korea Astronomy and Space Science Institute (KASI) (South Korea)
• Mexican Space Agency (AEM)
• National Aeronautics and Space Administration (NASA) (United States)
• Romanian Space Agency (ROSA)
• ROSCOSMOS (Russia)
• UK Space Agency (UKSA) (United Kingdom)

In addition to these members, several other organizations participate as permanent observers. These include the United Nations Office for Outer Space Affairs (UNOOSA), which serves as the group’s permanent secretariat and links it back to the UN, and IADWN, ensuring the “finders” and the “planners” are in constant communication.

How it Operates

SMPAG’s work is practical and task-oriented. It doesn’t just talk; it creates concrete “work plan items.” These are specific technical studies and reports assigned to different member agencies.

For example, a work plan item might be: “Analyze the mission requirements for a gravity tractor to deflect a 200-meter ‘rubble pile’ asteroid.” Another might be: “Define the payload characteristics of a generic reconnaissance spacecraft to determine an asteroid’s physical properties.”

By completing these tasks, SMPAG builds a shared library of technical knowledge. This ensures every agency is working from the same assumptions and understands the capabilities and limitations of different mitigation strategies. This shared understanding is perhaps SMPAG’s most important product.

The Other Half of the Shield: IADWN

It’s impossible to discuss SMPAG without further detailing its partner, the International Asteroid Warning Network (IADWN). The two groups are two sides of the same coin. IADWN’s output is SMPAG’s input.

The Global Telescope Network

IADWN is not a single, physical place. It’s a network of cooperation. Observatories around the world, both professional and (in some cases) advanced amateur, contribute their data. Major sky surveys, like the Catalina Sky Survey in Arizona or Pan-STARRS in Hawaii, automatically scan the sky every clear night. Their software flags any moving object not in existing catalogs.

This “new” object data is sent to the Minor Planet Center (MPC), a global clearinghouse operating under the International Astronomical Union (IAU). The MPC collects observations from all over the world, calculates a preliminary orbit, and posts it for other astronomers to see.

The Warning Protocol

Once an orbit is confirmed, automated systems at NASA‘s Jet Propulsion Laboratory (JPL) (the Sentry (monitoring system)) and ESA‘s Near-Earth Object Coordination Centre (NEOCC) (using the NEODyS system) take over. These systems project the orbit decades or even centuries into the future, checking for any potential close encounters or impacts with Earth.

If these systems detect a credible threat – one that exceeds a pre-defined probability and size threshold – the IADWN Steering Committee is convened. IADWN’s job is then to verify the data and, if the threat is real, to issue the official warning to the UN Office for OuterSpace Affairs (UNOOSA) and national governments.

This notification is the “starting gun” that formally activates SMPAG.

The Planetary Defense Playbook: SMPAG’s Core Functions

Once IADWN issues a warning, the focus shifts to SMPAG. Its members are the only ones with the hardware – the rockets, spacecraft, and technical teams – to do something about it. SMPAG’s core functions are to define when to act, what to do, and how to do it together.

Function 1: Establishing Thresholds for Action

SMPAG’s first job is to provide technical recommendations for when a mission is necessary. It’s not practical to launch a billion-dollar space mission for every small rock that has a 1-in-10,000 chance of hitting Earth.

SMPAG has established criteria, based on technical and programmatic factors, to guide political decision-makers. These criteria include:

• Impact Probability: Is the chance of impact greater than 1%?
• Object Size: Is the object larger than 50 meters in diameter?
• Warning Time: Is the potential impact less than 20 years away?

If a threat meets or exceeds these thresholds, SMPAG recommends that space agencies begin actively planning and preparing for a mitigation mission. For a more distant or uncertain threat, the recommendation might be to simply “monitor and characterize,” meaning, get more telescope data.

Function 2: Analyzing and Recommending Mitigation Options

This is the heart of SMPAG’s work. It assesses the different ways to deflect an asteroid. There is no single “best” solution; the right tool depends on the asteroid’s size, its composition, and, most importantly, the amount of warning time.

SMPAG focuses on the most technologically mature methods, which fall into three main categories.

Option 1: The Kinetic Impactor

The kinetic impactor is currently the most well-understood and technologically ready deflection method.

The Concept: This technique is a simple, elegant application of Newton’s laws of motion. You hit the asteroid with a heavy object (a spacecraft) traveling at very high speed (many kilometers per second).

It’s important to note that the goal is not to destroy the asteroid. Trying to blow up a large asteroid would likely just create a “shotgun blast” of smaller, equally dangerous fragments. The goal is to deflect it.

How it Works: The high-speed collision imparts momentum to the asteroid, slowing it down or speeding it up very slightly in its orbit. This tiny change in velocity (a “delta-v”) is all that’s needed. If you make this change years or decades before the predicted impact, that tiny nudge compounds over time. The asteroid will arrive at the point where Earth was minutes, hours, or days late (or early), missing our planet completely.

The DART Mission: A Real-World Test: This concept was spectacularly proven in 2022 by NASA’s Double Asteroid Redirection Test (DART) mission.

• The Target: The DART spacecraft traveled to a binary asteroid system named Didymos. Its target was the small 160-meter moonlet orbiting Didymos, an asteroid named Dimorphos.
• The Impact: On September 26, 2022, the washing-machine-sized DART spacecraft, traveling at over 6 km/s, slammed directly into Dimorphos.
• The Result: The success was greater than anyone expected. The impact changed Dimorphos’s orbital period around Didymos by 32 minutes. This was not just from the momentum of the spacecraft (the “kinetic” part) but also from a huge plume of rock and debris (ejecta) blasted into space, which acted like a rocket engine, giving the asteroid an extra push. This bonus push is called “momentum enhancement.”

The Follow-Up (Hera): The DART mission is a perfect example of the international cooperation SMPAG exists to foster. The European Space Agency (ESA) is now sending its own follow-up mission, Hera (spacecraft), which will arrive at the Didymos system in 2026. Hera will perform a detailed “crime scene investigation,” measuring Dimorphos’s new orbit precisely, studying the impact crater, and determining the asteroid’s mass and composition. This will allow scientists to fully understand the DART impact and turn the kinetic impactor method from a test into a well-understood, reliable engineering technique.

Option 2: The Gravity Tractor

For some scenarios, a kinetic impactor is too blunt an instrument. If the asteroid is a loosely-packed “rubble pile,” an impactor might just push through it without deflecting it much. Or, if we need an extremely precise nudge, an impactor’s effects are hard to predict perfectly.

The Concept: The gravity tractor is a more delicate, high-finesse method. It uses one of the most fundamental forces in the universe: gravity.

How it Works: A spacecraft is flown to the asteroid and then, using its own low-thrust engines, it “hovers” at a fixed position just above the surface (or alongside it). The spacecraft and the asteroid are now gravitationally bound. The spacecraft, even if it only weighs a few tons, has its own gravitational pull.

This tiny, almost imperceptible pull gently tugs on the asteroid. The spacecraft continuously fires its thrusters away from the asteroid to maintain its position, and in doing so, it slowly, slowly tows the entire asteroid with it.

Pros and Cons: The advantage of the gravity tractor is that it is 100% controllable and works on any kind of asteroid, whether it’s solid rock or a pile of gravel. The major disadvantage is that it is incredibly slow. The force is minuscule. A gravity tractor mission would need to be in place and towing for decades to achieve a meaningful deflection. This means it’s only an option for threats that we find with an exceptionally long warning time.

Option 3: The Nuclear Option

This is the one method everyone thinks of, thanks to Hollywood, and it’s the one SMPAG members treat with the most caution. Using a nuclear explosive device (NED) is the most powerful method available to humanity and is considered the “last resort” option.

It would only be considered for two scenarios:

1. A “Short-Warning” Threat: An object (perhaps a comet) is discovered only months or a few years before impact. There is no time for a kinetic impactor or gravity tractor to work.
2. A “City-Killer” or “Planet-Killer” Threat: The object is simply too large (many hundreds of meters or kilometers across) for a kinetic impactor to move.

SMPAG’s work clarifies that the “Hollywood” method – drilling into the asteroid and burying the bomb – is not the preferred approach. That is extremely difficult, risky, and likely to shatter the asteroid into many large, dangerous pieces.

The Standoff Detonation: The method studied by SMPAG members is the “standoff” detonation.

• How it Works: The nuclear device is flown to the asteroid and detonated at a specific distance from its surface, not on it.
• The Effect: The intense, instantaneous flash of X-rays and neutrons from the explosion hits one side of the asteroid. This energy instantly vaporizes a layer of the asteroid’s surface. This superheated vaporized rock expands violently, exploding off the surface. This massive, one-sided explosion of material acts like a giant rocket engine, giving the asteroid a powerful and rapid push.

Pros and Cons: The clear advantage is power. A nuclear standoff blast can deliver a “delta-v” (change in velocity) thousands of times greater than a kinetic impactor. It’s the only tool we have that could save us from a large object with a short warning time.

The disadvantages are immense. The Outer Space Treaty of 1967 explicitly bans placing “nuclear weapons or any other kinds of weapons of mass destruction” in orbit. Authorizing a planetary defense mission using a nuclear device would require an extraordinary international political and legal process, likely through the UN Security Council.

SMPAG’s role here is strictly apolitical. It provides the technical data: “For this size of threat with this warning time, a kinetic impactor will fail. A nuclear standoff detonation with this yield has a 95% chance of success.” It is up to the world’s political leaders to use that data.

Comparing the Mitigation Toolbox

SMPAG’s analysis of these options provides a clear framework for decision-making. The choice of tool is dictated entirely by the nature of the threat.

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The Mission Scenario: From Threat to Action

SMPAG and IADWN regularly conduct joint exercises, running through hypothetical threat scenarios to test their procedures. A real-world event would likely follow this simplified path:

1. Detection (IADWN): An observatory, perhaps the upcoming Vera C. Rubin Observatory in Chile, discovers a 250-meter asteroid.
2. Confirmation (IADWN): Other IADWN-linked telescopes confirm the object. The Minor Planet Center (MPC) calculates its orbit.
3. Risk Assessment (IADWN): NASA‘s Sentry (monitoring system) and ESA‘s NEODyS both calculate a 5% impact probability in 18 years, with the “risk corridor” (where it might hit) crossing Europe and Asia.
4. Official Warning (IADWN): The threat is confirmed and validated. IADWN officially notifies UNOOSA, which in turn informs all UN member states. The threat is now public and official.
5. Activation (SMPAG): SMPAG convenes an emergency meeting. The threat (250m size, 18-year lead time, 5% probability) clearly exceeds its pre-defined action thresholds.
6. Characterization (SMPAG Recommendation): SMPAG’s first recommendation is that the object must be characterized. We don’t know its composition. NASA and ESA are tasked with getting radar observations from facilities like the Goldstone Solar System Radar. JAXA proposes a fast flyby reconnaissance mission.
7. Mission Design (SMPAG): Radar and the flyby mission reveal the asteroid is a loosely-bound rubble pile. A kinetic impactor might be ineffective. With an 18-year lead time, a gravity tractor is too slow. The SMPAG working group determines the best option is a “kinetic impactor with an observer.” A heavy impactor will be sent, and a separate spacecraft will watch the impact to confirm the result.
8. Coordination (SMPAG Forum): This is where SMPAG’s function as a forum is vital. No single agency has to do it all. At the SMPAG meeting, a cooperative plan is formed:
   • NASA will provide the heavy kinetic impactor spacecraft, launching on a Falcon Heavy.
   • ESA will provide the observing spacecraft (like Hera), which will launch on an Ariane 6.
   • DLR and ASI will contribute key instruments for the observer.
   • UKSA and CNES will contribute to the mission’s navigation and data analysis.
9. Execution (National Agencies): The individual agencies go back to their governments, secure the funding, and build the hardware. The missions are launched.
10. Confirmation: The impact happens. The observer spacecraft confirms the asteroid’s orbit has been successfully altered. IADWN’s network of telescopes tracks the object for the next several years, and it is officially declared “safe.”

Challenges and Future Directions

SMPAG’s work is far from over. Significant technical and political challenges remain.

The Unknowns of Asteroids

The DART mission was a test on one type of asteroid. But as missions like NASA‘s OSIRIS-REx (which visited Bennu) and JAXA‘s Hayabusa2 (which visited Ryugu) have shown, asteroids are bizarre and diverse. Many are “rubble piles” that behave more like flying gravel banks than solid rocks. SMPAG needs more data on asteroid types to refine its models for kinetic impactors and nuclear devices.

The Lead Time Problem

All of our best methods rely on finding the threat early. The single most important part of planetary defense is building better telescopes. This is why SMPAG’s members are so invested in the next generation of surveys.

The Vera C. Rubin Observatory will survey the entire sky every few nights, cataloging millions of new objects. More importantly, space-based telescopes are needed. NASA‘s upcoming NEO Surveyor is a space-based infrared telescope. It will be able to find the dark, hard-to-see asteroids and, importantly, will be able to spot those (like Chelyabinsk) that approach from the direction of the Sun.

The Political and Legal Hurdles

SMPAG is a technical body, but it operates in a political world. The biggest challenges are not in the physics, but in the law and geopolitics.

• Liability: What if a deflection mission goes wrong? What if a kinetic impactor breaks an asteroid into pieces, one of which hits Brazil? Who is liable? The agency that built the impactor? The agency that launched it? All of SMPAG? The Space Liability Convention is not designed for this. SMPAG contributes to these discussions by providing the technical risk assessments.
• The Nuclear Taboo: The use of a nuclear device remains the most difficult political question. SMPAG’s work is to provide the objective, apolitical data to show if it’s the only option, but the decision to use it will have to be made at the highest levels of global government.

SMPAG and Public Communication

A key part of the UN mandate for both IADWN and SMPAG is public communication. If a credible threat is discovered, the world’s response will be as much a challenge in public policy as in engineering.

Averting panic is essential. The worst-case scenario is conflicting information from different sources, leading to public confusion, misinformation, and mistrust.

IADWN and SMPAG are designed to prevent this. IADWN acts as the single, clear voice for confirming the threat. SMPAG, in turn, acts as the single, unified technical voice for describing the solution. By communicating “what, when, and where” (IADWN) and “how” (SMPAG) through the official, calm channels of UNOOSA, the goal is to treat the problem as a manageable, solvable, global engineering challenge – not as a doomsday scenario.

Summary

The Space Mission Planning Advisory Group is one of the most important international organizations you’ve likely never heard of. It is not a world government or a global space agency. It doesn’t command fleets of spacecraft.

SMPAG is something more practical: a pre-planned agreement. It’s a “room” where the world’s best space engineers and planners meet to write the emergency procedures for a unique, high-consequence threat. It ensures that the technical, programmatic, and cooperative groundwork is already done before the emergency.

It provides the vital, apolitical, technical bridge between detecting a threat (IADWN’s job) and neutralizing it (the job of national space agencies). In a world often defined by competition, SMPAG is a quiet, powerful example of global cooperation. It represents humanity’s collective decision to move from being passive victims of cosmic chance to being active defenders of our own planet.