Level 1 — Absolute Beginner

A small robot is working in space. It flies around the Earth on a spacecraft. No people are with it. The robot has one arm, and it has a job. It builds things.

The robot takes thin tubes from a box. It takes small metal parts too. Then it joins them together. Slowly, it makes a strong frame. The frame looks a little like part of a bridge.

Scientists in California made the robot. They say this is a first. No machine has built a structure in space alone before. In the past, astronauts did this kind of work.

The scientists cannot talk to the robot all day. They can send orders for only 15 minutes each day. Then the robot works alone. Later, it sends photos to Earth, and the team checks the work.

robot

A machine that can do work by itself.

spacecraft

A vehicle that travels in space.

tubes

Long, thin, empty pieces of material.

joins

Puts two things together.

frame

The strong parts that give something its shape.

structure

Something that is built from many parts.

astronauts

People who travel and work in space.

orders

Words that tell someone what to do.

Level 2 — Elementary

Engineers at the California Institute of Technology, known as Caltech, say their robot has built part of a structure in orbit without any astronaut helping. The team believes it is the first time this has ever been done. The project is called ASTRA, and it is paid for by DARPA, a research agency of the United States military.

The robot travels on a small spacecraft that has been circling the Earth for about six months. Its mechanical arm picks up light tubes and metal joints from containers beside it. It connects them into square sections called bays. Several bays in a row make a truss, which is a strong frame like the ones in bridges and roofs.

The truss was launched with two bays already finished. In orbit, the robot built a third one. The complete design needs eleven bays, and the frame is meant to hold a reflector 1.4 meters wide, a little like a satellite dish.

The work was not easy. Engineers could contact the robot for only about 15 minutes a day, and they fixed several problems from the ground. The team does not expect to finish the whole truss before the mission ends in December. Still, the leader, Professor Sergio Pellegrino, calls the result a first for space construction.

orbit

The curved path of an object moving around a planet.

agency

A government office that does a special job.

mechanical

Worked by a machine, with moving parts.

joints

Parts that connect two pieces together.

containers

Boxes or other objects used to hold things.

truss

A strong frame made of connected bars.

launched

Sent into space.

reflector

A surface that sends light or signals back.

Level 3 — Intermediate

Building large things in space has always required people in spacesuits, or machines that simply unfold what was assembled on the ground. A team at the California Institute of Technology now reports a third way. Its ASTRA demonstration has used a robot to assemble part of a truss in low Earth orbit with no astronaut present. "This is the first time that a structure has been autonomously constructed in space," said Sergio Pellegrino, the Caltech professor who leads the project. The claim is the team's own and has not been independently confirmed.

ASTRA stands for Autonomous In-Space Tensioned Reflector Assembly. The hardware flew as a payload on Vigoride 7, a space tug operated by the company Momentus, and has spent about six months in orbit. The demonstration is funded by DARPA, the Pentagon's research agency, under a program that studies new materials and manufacturing methods for space.

The principle is repetition. A robotic arm collects composite fiber tubes and aluminum joints from nearby dispensers and locks them together into identical sections, or bays, that form a perimeter truss. Two bays were built before launch and deployed in orbit, and the robot then completed a third. The finished ring would need eleven and would support a reflector 1.4 meters across, with a surface made of Kapton film. According to reports, controllers could send commands only during short communication windows that added up to roughly 15 minutes a day, and they judged progress from downloaded photographs.

The mission has not gone perfectly. The team speaks of many "little surprises" that had to be solved from the ground, and it does not expect to complete the truss before operations end in December. The significance lies elsewhere. Rockets limit the size of anything launched in one piece. If machines can assemble structures after launch, antennas and telescopes could one day be far larger than any rocket could carry.

assemble

To put the parts of something together.

autonomously

Without direct control by a person.

payload

The equipment that a spacecraft carries.

composite

Made from two or more different materials.

dispensers

Containers that release items one at a time.

perimeter

The outer edge around a shape or area.

deployed

Opened out and put into use.

significance

The importance or meaning of something.

Level 4 — Advanced

Every large object humanity has placed in orbit has been constrained by the same bottleneck: it had to fit inside a rocket fairing. The James Webb Space Telescope solved the problem with origami, folding a 6.5-meter mirror to fit a shroud little more than five meters wide, at enormous cost and risk. The International Space Station solved it with astronauts and more than a decade of spacewalks. A modest experiment run from Pasadena points to a different answer. Caltech's ASTRA demonstration has, its engineers say, assembled a section of structural truss in low Earth orbit using a robot acting without a human in the loop.

The claim, voiced by project leader Sergio Pellegrino, is that this is "the first time that a structure has been autonomously constructed in space". It deserves the usual caution attached to self-reported firsts. Yet the technical account is specific. The payload, carried on a Momentus Vigoride 7 tug and funded through DARPA's program on novel orbital manufacturing, consists of a builder arm, dispensers of composite struts and aluminum nodes, and the beginnings of a perimeter truss intended to tension a 1.4-meter Kapton reflector. Two bays went up prefabricated. The robot added a third.

What makes the feat harder than it sounds is the poverty of supervision. Controllers reportedly had contact for a cumulative quarter of an hour each day, far too little to steer the arm in real time, and verified each step retrospectively from downlinked images. The system therefore had to execute sequences of grasping, aligning and latching on its own, in an environment where a dropped part cannot be retrieved and thermal swings distort every tolerance. The team concedes a series of "little surprises", and with eleven bays required and the mission closing in December, the ring will almost certainly remain unfinished.

That shortfall matters less than the proof of principle. Repetitive assembly from standardized elements scales in a way that folding does not. In theory, a builder could keep adding bays long after a deployable design would have exhausted its packaging tricks. Pellegrino has pointed to astronomy, astrophysics and communications as beneficiaries, and it is no accident that a defense agency is paying. Apertures tens of meters wide would transform radio astronomy and surveillance alike. One bay is a small beginning, but it is a different kind of beginning.

constrained

Limited or restricted by something.

bottleneck

A narrow point that slows a whole process down.

fairing

The protective nose cover at the top of a rocket.

prefabricated

Built in advance, before being taken to its final place.

cumulative

Added together over a period of time.

retrospectively

Looking back at something after it has happened.

tolerance

The small amount by which a measurement is allowed to vary.