NASA has earmarked October 20 as the date it will endeavour to land the first human craft on an asteroid.
The space agency announced its OSIRIS-REx craft will touch down for a handful of seconds on asteroid Bennu following a carefully orchestrated 4.5 hour descent.
NASA has already picked its landing site, dubbed Nightingale, a rocky area 52 ft (16 m) in diameter in Bennu's northern hemisphere.
The van-sized craft is fitted with a robotic arm which will attempt to collect samples of the surface.
Scientists hope the mission will deepen our understanding of how planets formed and life began and provide insight on asteroids that could impact Earth.
The space agency announced its OSIRIS-REx craft will touch down for a handful of seconds on asteroid Bennu following a carefully orchestrated 4.5 hour descent. Pictured, artist's impression
The Nightingale site has been chosen because it poses one of the clearest areas on the asteroid's surface with best access to fine-grained material.
However, there are building-sized boulders surrounding the site, leaving a spot the size of only a few parking spots in which to land.
If the landing goes even slightly awry, OSIRIS-REx will find itself in treacherous territory.
Bennu sits between Earth and Mars at a distance approximately 207 million miles (334 million kilometers) from our planet.
Because of this, it will take about 18.5 minutes for signals to travel between OSIRIS-REx and NASA headquarters.
This means a manual landing is impossible, with all hopes of a successful landing hinging on the on-board autonomous system.
OSIRIS-REx is supposed to collect at least 2 ounces (57 grams) of Bennu's rocky material to bring back to Earth.
This will be the largest sample selection since the Apollo missions, which had the bonus of much more funding and humans on the surface to aid collection.
Should the collection of Bennu's surface material be successful, it will be returned to Earth on September 24, 2023.
NASA revealed some details on how the OSIRIS-Rex craft will land on Bennu.
The 4.5-hour ordeal will be broken down into three distinct maneuvers.
The first will involve a firing of the thrusters on OSIRIS-REx to take it out of orbit, around 2,500 feet (770 meters) above the surface.
This low altitude is due to the tiny gravitational pull of the asteroid, which is less than a third of a mile across.
At this point, the robotic sampling arm, the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), will unfurl and point down towards Bennu.
Its fragile solar panels will move into a Y-wing orientation above the spacecraft, safely out the way of any hazards.
The TAG head is the only part of the spacecraft that will come into contact with Bennu's surface.
'Years of planning and hard work by this team are essentially coming down to putting the TAGSAM (Touch-And-Go Sample Acquisition Mechanism) into contact with the surface for just five to 10 seconds,' said Mike Moreau, OSIRIS-REx deputy project manager.
NASA revealed some details on how the OSIRIS-Rex craft will land on Bennu and the 4.5 hour ordeal will be broken down into three distinct maneuvers. The first will involve a firing of the thrusters on OSIRIS-REx to take it out of orbit, around 2,500 feet (770 meters) above the surface
NASA previously spotted pieces of asteroid Vesta ranging in size from five to 14 feet scattered across Bennu's southern hemisphere and near its center (pictured)
NASA images of asteroid Bennu reveal 'extremely bright' chunks of another asteroid on the surface
NASA spotted pieces of asteroid Vesta ranging in size from five to 14 feet scattered across Bennu's southern hemisphere and near its center.
The boulders were detected in images from the OSIRIS-Rex and appear much brighter than the surrounding area of dark, rich carbon.
The team analyzed the chunks using an on-board spectrometer and found signs of the mineral pyroxene - a known compound on Vesta.
NASA theorizes the material came from Bennu's parent asteroid that was struck by a fragment from Vesta.
Hannah Kaplan of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said: 'Our leading hypothesis is that Bennu inherited this material from its parent asteroid after a vestoid (a fragment from Vesta) struck the parent.'
'Then, when the parent asteroid was catastrophically disrupted, a portion of its debris accumulated under its own gravity into Bennu, including some of the pyroxene from Vesta.'
NASA will authorise the descent and allow OSIRIS-REx to take control of its own landing, using a system called Natural Feature Tracking (NFT) navigation system.
This uses all the detailed images the mission has taken of the asteroid's surface and turns it into a map, pointing out all potential hazards.
It is pre-programmed to abort the mission if it strays outside of various pre-defined limits which may put it at risk.
Should this happen, NASA will regroup and attempt the mission again at a later date, it said.
A slow and steady descent will take around four hours, before a so-called 'Checkpoint' maneuver at an approximate altitude of 410 ft (125 m).
The gradual decline will be replaced with a steeper and faster approach to the surface following yet another blast from the thrusters.
Around 11 minutes later, the third and final maneuver, called 'Matchpoint', will occur. Here, the computer system will use the thrusters and attempt to stabilise the craft just 177 ft (54 m) above the landing site.
OSIRIS-Rex will again slow down and attempt to match the spin of the asteroid before its approach.
It will touch down on the surface for no more than 16 seconds, NASA predicts.
It will then eject gas from an on-board nitrogen bottle to fling up debris from Bennu's surface.
The spacecraft will try and collect some of this detritus before firing, yet again, its thrusters to retreat back to the safety of orbit.
NASA will not know until the week after the landmark landing if it was successful in obtaining the target of 2 ounces (60 grams) of material.
On October 22, an on-board camera will take photos of the extendable arm to see if any material was collected.
On October 24, OSIRIS-REx will try and determine the mass of the material.
If it is deemed adequate, it will be safely packaged up in the Sample Return Capsule (SRC) for a trip to Earth.
If NASA is displeased, it will simply go back and try again, as OSIRIS-REx has enough nitrogen for three total attempts.
If this should happen, NASA would ditch Nightingale and target the back-up site, Osprey, and not go again until January 2021 at the earliest.
HOW WILL NASA'S OSIRIS-REX MISSION TO TAKE SAMPLES FROM AN ASTEROID WORK?
Osiris-Rex is the first US mission designed to return a piece of an asteroid to Earth.
Scientists say the ancient asteroid could hold clues to the origin of life.
It's believed to have formed 4.5 billion years ago, a remnant of the solar system's building blocks.
After a careful survey of Bennu to characterise the asteroid and locate the most promising sample sites, Osiris-Rex will collect between 2 and 70 ounces (about 60 to 2,000 grams) of surface material with its robotic arm and return the sample to Earth via a detachable capsule in 2023.
To capture samples on the surface, the craft will hover over a specific area and 'will be sent down at a very slow and gently' 4 inches (10 cm) per second.
The spacecraft will also carry a laser altimeter, a suite of cameras provided by the University of Arizona, spectrometers and lidar, which is similar to radar, using light instead of radio waves to measure distance.
The asteroid Bennu, as photographed by OSIRIS-REx, on December 2, 2018