There are many reasons not to allow the two satellite radio companies — Sirius and XM — to merge. The benefits of having at least two companies providing satellite-delivered radio are manifest in the companies themselves. Their intense competition has driven rapid innovation in receiver technology — and rather less innovation in content.

Another reason should lie near and dear to the spacecraft manufacturing and launch industries: the loss of a significant customer for new spacecraft and, more importantly, of satellite network diversity.

At first glance, it is difficult to tell the two companies’ programming apart. Both offer many tens of popular music and sports stations almost as bland as those on terrestrial radio, and precious little in the way of true niche programming. That said, satellite radio has made available an unprecedented variety of news programming. This is especially so for rural customers who, in the past, have had few real choices. Diversity of news and opinion is vital for a healthy democracy.

If one company were to drop, say, the BBC News, it might be possible to find it on the other. If a merged company were to drop an important program, the listener, and particularly the rural listener or one traveling in their car at the suburban edge, would have few if any options.

Much of the programming may be all too similar, but it is rarely appreciated just how different the two companies’ satellite networks are. This matters for a number of reasons.

Sirius and XM will have to maintain their separate constellations for many years to avoid disrupting service. This greatly reduces the near-term financial benefits of any merger, which should require a correspondingly larger public benefit to allow the merger to go forward. However, XM’s Chairman Gary Parsons admitted that eventually the companies will settle on a single constellation — which creates its own problems.

XM’s satellite fleet is in geostationary orbit over the equator, in theory requiring fewer and more conventional spacecraft than the competition. Since the satellites remain fixed in the sky, XM gets by with simpler, and presumably cheaper, consumer receivers.

Unfortunately, satellites over the equator look at North America at a sharp angle — the further north you are, the sharper the angle. That necessitates a large and expensive national network of repeaters to allow uninterrupted reception in the mountains and in urban canyons — any place where the consumer receiver cannot directly see the sky above the equator. In rural areas without the population density to support terrestrial repeaters, reception inevitably will be relatively poor.

Sirius’ three spacecraft are in highly elliptical Molniya -type orbits, which were invented by the Soviet military to allow constant communications with deployed forces at high latitudes. The Sirius satellites have the high point in their orbits directly over North America, and their low points on the opposite side of the planet. A satellite travels slower when it is high above the planet, so Sirius’s spacecraft spend most of their time high above North America looking down onto the United States – deep into those natural and urban canyons. Careful spacing of three satellites so that one is always near the high-point of its orbit allows continuous service to be maintained. Far fewer expensive ground repeaters are needed.

Requiring a minimum of three high-capacity spacecraft plus spares, to XM’s theoretical minimum of one, Sirius’ space segment is more unusual and probably more expensive to launch and maintain. Worse, since they have to track spacecraft moving across the sky, Sirius’ receivers are more complex: resolving technical problems with the receivers was the key reason that the first company to get started, Sirius, was late to market. This allowed Johnny-come-lately XM to achieve an early market dominance.

The more northern and rural one is, the more clear the Sirius advantage. This can be seen in the Canadian market, throughout much of which XM’s satellites appear close above the horizon. It is worth noting that Sirius has consistently out-sold XM in Canada — although better marketing and programming more attractive to Canadians are probably the major reasons.

As currently constituted, Sirius’ space segment is more fragile than XM’s. There is less excess and spare capacity, what there is sits on the ground, and Sirius’ satellites are older. Were Sirius to suddenly lose a satellite — a rare event in fully deployed spacecraft, but hardly unheard of — service undoubtedly would be disrupted until the ground spare could be prepared and flown. In today’s launch market, with little unclaimed launch capacity, that could take some time.

Ignoring all of the advantages of their current constellation, Sirius recently ordered a new spacecraft for geostationary orbit. Since Sirius management has been driving the effort toward consolidation, this may have been intended to start the long process of uniting the very different space segments of the two companies around XM’s younger satellites.

As things stand, if one company’s space segment were to catastrophically break down, the other’s would be there to replace it. If a merged company were to mismanage its space segment, there would be no backup. At least temporarily, the United States could lose satellite radio service and many of the billions of dollars so far invested.

Preserving programmatic and corporate diversity are important reasons for opposing the merger of Sirius and XM, but preserving space segment diversity is even more so. For the sake of rural radio listeners and those on the suburban edge — and especially to preserve high-quality service in northern areas of the United States and for our neighbors in Canada — the Federal Communications Commission should oppose this merger.

Moreover, the FCC should strongly encourage Sirius to maintain their Molniya -type satellite network and to decrease its fragility with additional satellites.

Donald F. Robertson is a freelance space industry journalist based in San Francisco. He is a customer of Sirius and owns stock in both Sirius and XM.